O-RINGS

O-Ring O-rings are so-named because they are circular sealing rings that resemble the letter "O." They have a round cross section like a doughnut or torus (cross section refers to the cut end of an o-ring, which is round). In a U.S. patent dated November 21, 1939, Niels A. Christensen described the "resilient packing ring" as being suitable for use "as a packing for fluid medium pistons whether the fluid be liquid or air." O-rings are said to be the predominate type of seal in use today and the first type considered for new designs because they are inexpensive, easy to use and reliable.

Remarkably versatile, o-rings are found in a wide variety of axial and radial static (non-moving, gasket-type) and dynamic (oscillating, reciprocating and rotating) applications. They are used as bumpers, couplers, grommets, low torque drive belts, rollers, shock absorbers, vibration dampers and wheels. They are employed in air conditioning, brake, cooling, emission control, fuel, hydraulic, power steering and vacuum systems and in automatic transmissions, engines, faucet valves and pumps. They act as seals for caps, connectors, flanges, pistons, plugs, rods and as straight thread tube fitting boss gaskets.

Usually made from an elastic synthetic material that resembles rubber, called an elastomer, o-rings often seat in a groove and provide an effective seal when compressed (opposite sides of the o-ring are squeezed between two surfaces). Common cross section compression is 10 to 40% for static seals and 10 to 30% for dynamic. In addition, o-rings should be slightly stretched—from 1 to 5% maximum, with 2% often being ideal—to ensure a snug fit in the groove. If the amount of inside diameter stretch exceeds 5%, a reduction in cross section and corresponding decrease in compression can compromise the effectiveness of the seal and cause the o-ring to age prematurely due to stress. However, o-rings used for floating seals, which allow some leakage to reduce friction, may "float" (move freely) in the groove.

O-rings are available in a wide range of standard sizes. Their size is often specified as inside diameter (ID) and cross section (CS) diameter or width. Outside diameter (OD) may also be specified, but it can be easily calculated if needed: OD = ID + 2 x CS. If ID and OD are known, CS is easy to determine—it is half the difference of OD and ID: CS = (OD - ID) / 2. Nominal o-ring size is usually specified in fractional inches, while actual size is in decimal inches. Size may also be specified as a three digit identification code, called a "dash number"—"120" for example—as defined by AS568A, Aerospace Size Standard for O-Rings, which is generally agreed to be the reference for standard U.S. sizes. See Tables 1 through 5 for a listing of AS568A "dash numbers." (As of this writing, AS568C is the current version, but many still refer to the standard as AS568A.)

Cross section size for most of the 000 series is 1/16" nominal (0.070" actual); the 100 series is 3/32" (0.103"); 200 series is 1/8" (0.139"); 300 series is 3/16" (0.210"); and the 400 series is 1/4" nominal (0.275" actual).

Common inside diameters range from 3/64" to 3" for 1/16" cross section; 3/16" to 6" for 3/32" CS; 3/16" to 8 1/4" for 1/8" CS; 3/4" to 6" for 3/16" CS; and 4 1/2" to 5 7/8" ID for 1/4" cross section.

Different materials exhibit different physical properties while allowing o-rings to resist different chemicals and operate over different temperature ranges. Two common materials are Buna-N and Viton®. Since ratings serve as a general guideline only, be sure to test the material in the actual application to verify suitability. See Table 6 for a comparison of physical properties and Table 7 for a summary of chemical resistance.

Buna-N

, also known as Nitrile and referred to by its ASTM D1418 designation of NBR, is popular because of its low cost, physical properties and resistance to certain chemicals. It is the most widely used material and its cost is the lowest of the oil resistant elastomers. In terms of physical properties, abrasion resistance is considered excellent; tensile strength, elongation, low temperature flexibility, compression set, tear resistance and gas permeability are rated as good; flame resistance, however, is poor. Chemical resistance to water, petroleum oil and silicone lubricants is excellent; dilute acids, dilute alkalis, hydraulic fluids and transmission fluid is good; steam is fair; but resistance to ozone, weather, ketones, strong acids and brake fluid is poor. Exposure to direct sunlight will cause rapid deterioration as will moderate to high levels of atmospheric ozone. Operating temperature range is -40° to +250°F.

Viton®

, a trade name and registered trademark of DuPont, is also called Fluorocarbon and known by its ASTM D1418 designation of FKM. It is often used in automotive engine compartments because of its extended resistance to petroleum oils at high operating temperatures. Said to "approach the ideal for a universal o-ring material," it is unusually resistant to embrittlement when exposed to elevated temperatures for prolonged periods, and "is considered to be serviceable indefinitely when exposed continuously to 200°C." It also resists swell when exposed to non-leaded gasoline. Physical properties such as compression set, flame resistance and gas permeability are excellent; tensile strength and abrasion resistance are good; elongation and tear resistance are fair; but low temperature flexibility is poor. Chemical resistance to ozone, weather, water, dilute acids, dilute alkalis, petroleum oils and solvents is excellent; steam and ketones is fair; anhydrous ammonia, though, is poor. Its operating temperature is a wide -15° to +400°F.

Durometer is both an instrument and a unit of measure for hardness. In U.S. patent applications between 1924 and 1930, Albert F. Shore described his invention as an Apparatus for Measuring the Hardness of Materials, now known as the durometer. Specified in points, as determined by the depth a hardened indenter penetrates the material under test, each measurement point equals 0.0025 mm of penetration. The durometer scale runs from 0 (softest) to 100 (hardest); for o-rings, the measurement is usually based on the Shore A scale (there are at least nine other uncorrelated scales). A common rating for Buna-N is 70 whereas 75 is the base rating for Viton®. You may see "A" as a prefix or suffix to the durometer rating—such as A70 or 70A—or "Shore A" before or after the rating to indicate that it is referenced to the Shore A scale. While harder materials better resist wear, they are also less flexible.

Although simple to install, the following recommendations will help prevent premature o-ring failure…

Make sure all surfaces the o-ring will contact are clean.
Lightly coat o-rings with a lubricant that is compatible with the o-ring material and system chemicals, keeping in mind that "like dissolves like" (for example, don't use a silicone lubricant with a silicone o-ring).
Do not use a lubricant that causes the o-ring to shrink or swell excessively.
Stretch o-rings uniformly and not more than 100% during installation.
Remove twists once the o-ring is seated.
Use tape or a thimble to protect o-rings from sharp edges such as threads.
Avoid excessive twisting when folding o-rings for insertion into internal grooves.
O-rings can be damaged if pistons are twisted into cylinders.

While surface lubrication helps to protect o-rings during installation, it also improves seal performance in pneumatic and vacuum applications by filling micropores in the o-rings and mating surfaces. Lubrication also extends the service life of o-rings by protecting them from exposure to oxygen and ozone.

When specifying o-rings, be sure to confirm inside (hole) diameter, cross section (width), durometer (hardness) and material type. Typical reasons for o-ring failure include incorrect o-ring size, the o-ring material is not compatible with system chemicals, and improper o-ring installation and lubrication.

Refer to Tables 1 through 5 for AS568A dash numbers, actual size and nominal size of o-rings. All dimensions are in inches. Nominal sizes are fractional inch approximations of actual decimal sizes and are for reference only.

**Table 1. O-Ring Size Chart for 000 Series.** AS568A designation, actual size and nominal size. Dimensions are in inches. (Note: Nominal size is approximate and for reference only.)
O-Ring Size Chart 1
000 Series Cross Section: 1/16" (0.040" ~ 0.070" ±0.003")
AS568A Dash Number	Actual Size			Nominal Size
AS568A Dash Number	ID	ID ±	CS	ID	OD	CS
001	0.029	0.004	0.040	1/32	3/32	1/32
002	0.042	0.004	0.050	3/64	9/64	3/64
003	0.056	0.004	0.060	1/16	3/16	1/16
004	0.070	0.005	0.070	5/64	13/64	1/16
005	0.101	0.005	0.070	3/32	7/32	1/16
006	0.114	0.005	0.070	1/8	1/4	1/16
007	0.145	0.005	0.070	5/32	9/32	1/16
008	0.176	0.005	0.070	3/16	5/16	1/16
009	0.208	0.005	0.070	7/32	11/32	1/16
010	0.239	0.005	0.070	1/4	3/8	1/16
011	0.301	0.005	0.070	5/16	7/16	1/16
012	0.364	0.005	0.070	3/8	1/2	1/16
013	0.426	0.005	0.070	7/16	9/16	1/16
014	0.489	0.005	0.070	1/2	5/8	1/16
015	0.551	0.007	0.070	9/16	11/16	1/16
016	0.614	0.009	0.070	5/8	3/4	1/16
017	0.676	0.009	0.070	11/16	13/16	1/16
018	0.739	0.009	0.070	3/4	7/8	1/16
019	0.801	0.009	0.070	13/16	15/16	1/16
020	0.864	0.009	0.070	7/8	1	1/16
021	0.926	0.009	0.070	15/16	1 1/16	1/16
022	0.989	0.010	0.070	1	1 1/8	1/16
023	1.051	0.010	0.070	1 1/16	1 3/16	1/16
024	1.114	0.010	0.070	1 1/8	1 1/4	1/16
025	1.176	0.011	0.070	1 3/16	1 5/16	1/16
026	1.239	0.011	0.070	1 1/4	1 3/8	1/16
027	1.301	0.011	0.070	1 5/16	1 7/16	1/16
028	1.364	0.013	0.070	1 3/8	1 1/2	1/16
029	1.489	0.013	0.070	1 1/2	1 5/8	1/16
030	1.614	0.013	0.070	1 5/8	1 3/4	1/16
031	1.739	0.015	0.070	1 3/4	1 7/8	1/16
032	1.864	0.015	0.070	1 7/8	2	1/16
033	1.989	0.018	0.070	2	2 1/8	1/16
034	2.114	0.018	0.070	2 1/8	2 1/4	1/16
035	2.239	0.018	0.070	2 1/4	2 3/8	1/16
036	2.364	0.018	0.070	2 3/8	2 1/2	1/16
037	2.489	0.018	0.070	2 1/2	2 5/8	1/16
038	2.614	0.020	0.070	2 5/8	2 3/4	1/16
039	2.739	0.020	0.070	2 3/4	2 7/8	1/16
040	2.864	0.020	0.070	2 7/8	3	1/16
041	2.989	0.024	0.070	3	3 1/8	1/16
042	3.239	0.024	0.070	3 1/4	3 3/8	1/16
043	3.489	0.024	0.070	3 1/2	3 5/8	1/16
044	3.739	0.027	0.070	3 3/4	3 7/8	1/16
045	3.989	0.027	0.070	4	4 1/8	1/16
046	4.239	0.030	0.070	4 1/4	4 3/8	1/16
047	4.489	0.030	0.070	4 1/2	4 5/8	1/16
048	4.739	0.030	0.070	4 3/4	4 7/8	1/16
049	4.989	0.037	0.070	5	5 1/8	1/16
050	5.239	0.037	0.070	5 1/4	5 3/8	1/16

**Table 2. O-Ring Size Chart for 100 Series.** AS568A designation, actual size and nominal size. Dimensions are in inches. (Note: Nominal size is approximate and for reference only.)
O-Ring Size Chart 2
100 Series Cross Section: 3/32" (0.103" ±0.003")
AS568A Dash Number	Actual Size			Nominal Size
AS568A Dash Number	ID	ID ±	CS	ID	OD	CS
102	0.049	0.005	0.103	1/16	1/4	3/32
103	0.081	0.005	0.103	3/32	9/32	3/32
104	0.112	0.005	0.103	1/8	5/16	3/32
105	0.143	0.005	0.103	5/32	11/32	3/32
106	0.174	0.005	0.103	3/16	3/8	3/32
107	0.206	0.005	0.103	7/32	13/32	3/32
108	0.237	0.005	0.103	1/4	7/16	3/32
109	0.299	0.005	0.103	5/16	1/2	3/32
110	0.362	0.005	0.103	3/8	9/16	3/32
111	0.424	0.005	0.103	7/16	5/8	3/32
112	0.487	0.005	0.103	1/2	11/16	3/32
113	0.549	0.007	0.103	9/16	3/4	3/32
114	0.612	0.009	0.103	5/8	13/16	3/32
115	0.674	0.009	0.103	11/16	7/8	3/32
116	0.737	0.009	0.103	3/4	15/16	3/32
117	0.799	0.010	0.103	13/16	1	3/32
118	0.862	0.010	0.103	7/8	1 1/16	3/32
119	0.924	0.010	0.103	15/16	1 1/8	3/32
120	0.987	0.010	0.103	1	1 3/16	3/32
121	1.049	0.010	0.103	1 1/16	1 1/4	3/32
122	1.112	0.010	0.103	1 1/8	1 5/16	3/32
123	1.174	0.012	0.103	1 3/16	1 3/8	3/32
124	1.237	0.012	0.103	1 1/4	1 7/16	3/32
125	1.299	0.012	0.103	1 5/16	1 1/2	3/32
126	1.362	0.012	0.103	1 3/8	1 9/16	3/32
127	1.424	0.012	0.103	1 7/16	1 5/8	3/32
128	1.487	0.012	0.103	1 1/2	1 11/16	3/32
129	1.549	0.015	0.103	1 9/16	1 3/4	3/32
130	1.612	0.015	0.103	1 5/8	1 13/16	3/32
131	1.674	0.015	0.103	1 11/16	1 7/8	3/32
132	1.737	0.015	0.103	1 3/4	1 15/16	3/32
133	1.799	0.015	0.103	1 13/16	2	3/32
134	1.862	0.015	0.103	1 7/8	2 1/16	3/32
135	1.925	0.017	0.103	1 15/16	2 1/8	3/32
136	1.987	0.017	0.103	2	2 3/16	3/32
137	2.050	0.017	0.103	2 1/16	2 1/4	3/32
138	2.112	0.017	0.103	2 1/8	2 5/16	3/32
139	2.175	0.017	0.103	2 3/16	2 3/8	3/32
140	2.237	0.017	0.103	2 1/4	2 7/16	3/32
141	2.300	0.020	0.103	2 5/16	2 1/2	3/32
142	2.362	0.020	0.103	2 3/8	2 9/16	3/32
143	2.425	0.020	0.103	2 7/16	2 5/8	3/32
144	2.487	0.020	0.103	2 1/2	2 11/16	3/32
145	2.550	0.020	0.103	2 9/16	2 3/4	3/32
146	2.612	0.020	0.103	2 5/8	2 13/16	3/32
147	2.675	0.022	0.103	2 11/16	2 7/8	3/32
148	2.737	0.022	0.103	2 3/4	2 15/16	3/32
149	2.800	0.022	0.103	2 13/16	3	3/32
150	2.862	0.022	0.103	2 7/8	3 1/16	3/32
151	2.987	0.024	0.103	3	3 3/16	3/32
152	3.237	0.024	0.103	3 1/4	3 7/16	3/32
153	3.487	0.024	0.103	3 1/2	3 11/16	3/32
154	3.737	0.028	0.103	3 3/4	3 15/16	3/32
155	3.987	0.028	0.103	4	4 3/16	3/32
156	4.237	0.030	0.103	4 1/4	4 7/16	3/32
157	4.487	0.030	0.103	4 1/2	4 11/16	3/32
158	4.737	0.030	0.103	4 3/4	4 15/16	3/32
159	4.987	0.035	0.103	5	5 3/16	3/32
160	5.237	0.035	0.103	5 1/4	5 7/16	3/32
161	5.487	0.035	0.103	5 1/2	5 11/16	3/32
162	5.737	0.035	0.103	5 3/4	5 15/16	3/32
163	5.987	0.035	0.103	6	6 3/16	3/32
164	6.237	0.040	0.103	6 1/4	6 7/16	3/32
165	6.487	0.040	0.103	6 1/2	6 11/16	3/32
166	6.737	0.040	0.103	6 3/4	6 15/16	3/32
167	6.987	0.040	0.103	7	7 3/16	3/32
168	7.237	0.045	0.103	7 1/4	7 7/16	3/32
169	7.487	0.045	0.103	7 1/2	7 11/16	3/32
170	7.737	0.045	0.103	7 3/4	7 15/16	3/32
171	7.987	0.045	0.103	8	8 3/16	3/32
172	8.237	0.050	0.103	8 1/4	8 7/16	3/32
173	8.487	0.050	0.103	8 1/2	8 11/16	3/32
174	8.737	0.050	0.103	8 3/4	8 15/16	3/32
175	8.987	0.050	0.103	9	9 3/16	3/32
176	9.237	0.055	0.103	9 1/4	9 7/16	3/32
177	9.487	0.055	0.103	9 1/2	9 11/16	3/32
178	9.737	0.055	0.103	9 3/4	9 15/16	3/32

**Table 3. O-Ring Size Chart for 200 Series.** AS568A designation, actual size and nominal size. Dimensions are in inches. (Note: Nominal size is approximate and for reference only.)
O-Ring Size Chart 3
200 Series Cross Section: 1/8" (0.139" ±0.004")
AS568A Dash Number	Actual Size			Nominal Size
AS568A Dash Number	ID	ID ±	CS	ID	OD	CS
201	0.171	0.005	0.139	3/16	7/16	1/8
202	0.234	0.005	0.139	1/4	1/2	1/8
203	0.296	0.005	0.139	5/16	9/16	1/8
204	0.359	0.005	0.139	3/8	5/8	1/8
205	0.421	0.005	0.139	7/16	11/16	1/8
206	0.484	0.005	0.139	1/2	3/4	1/8
207	0.546	0.007	0.139	9/16	13/16	1/8
208	0.609	0.009	0.139	5/8	7/8	1/8
209	0.671	0.009	0.139	11/16	15/16	1/8
210	0.734	0.010	0.139	3/4	1	1/8
211	0.796	0.010	0.139	13/16	1 1/16	1/8
212	0.859	0.010	0.139	7/8	1 1/8	1/8
213	0.921	0.010	0.139	15/16	1 3/16	1/8
214	0.984	0.010	0.139	1	1 1/4	1/8
215	1.046	0.010	0.139	1 1/16	1 5/16	1/8
216	1.109	0.012	0.139	1 1/8	1 3/8	1/8
217	1.171	0.012	0.139	1 3/16	1 7/16	1/8
218	1.234	0.012	0.139	1 1/4	1 1/2	1/8
219	1.296	0.012	0.139	1 5/16	1 9/16	1/8
220	1.359	0.012	0.139	1 3/8	1 5/8	1/8
221	1.421	0.012	0.139	1 7/16	1 11/16	1/8
222	1.484	0.015	0.139	1 1/2	1 3/4	1/8
223	1.609	0.015	0.139	1 5/8	1 7/8	1/8
224	1.734	0.015	0.139	1 3/4	2	1/8
225	1.859	0.018	0.139	1 7/8	2 1/8	1/8
226	1.984	0.018	0.139	2	2 1/4	1/8
227	2.109	0.018	0.139	2 1/8	2 3/8	1/8
228	2.234	0.020	0.139	2 1/4	2 1/2	1/8
229	2.359	0.020	0.139	2 3/8	2 5/8	1/8
230	2.484	0.020	0.139	2 1/2	2 3/4	1/8
231	2.609	0.020	0.139	2 5/8	2 7/8	1/8
232	2.734	0.024	0.139	2 3/4	3	1/8
233	2.859	0.024	0.139	2 7/8	3 1/8	1/8
234	2.984	0.024	0.139	3	3 1/4	1/8
235	3.109	0.024	0.139	3 1/8	3 3/8	1/8
236	3.234	0.024	0.139	3 1/4	3 1/2	1/8
237	3.359	0.024	0.139	3 3/8	3 5/8	1/8
238	3.484	0.024	0.139	3 1/2	3 3/4	1/8
239	3.609	0.028	0.139	3 5/8	3 7/8	1/8
240	3.734	0.028	0.139	3 3/4	4	1/8
241	3.859	0.028	0.139	3 7/8	4 1/8	1/8
242	3.984	0.028	0.139	4	4 1/4	1/8
243	4.109	0.028	0.139	4 1/8	4 3/8	1/8
244	4.234	0.030	0.139	4 1/4	4 1/2	1/8
245	4.359	0.030	0.139	4 3/8	4 5/8	1/8
246	4.484	0.030	0.139	4 1/2	4 3/4	1/8
247	4.609	0.030	0.139	4 5/8	4 7/8	1/8
248	4.734	0.030	0.139	4 3/4	5	1/8
249	4.859	0.035	0.139	4 7/8	5 1/8	1/8
250	4.984	0.035	0.139	5	5 1/4	1/8
251	5.109	0.035	0.139	5 1/8	5 3/8	1/8
252	5.234	0.035	0.139	5 1/4	5 1/2	1/8
253	5.359	0.035	0.139	5 3/8	5 5/8	1/8
254	5.484	0.035	0.139	5 1/2	5 3/4	1/8
255	5.609	0.035	0.139	5 5/8	5 7/8	1/8
256	5.734	0.035	0.139	5 3/4	6	1/8
257	5.859	0.035	0.139	5 7/8	6 1/8	1/8
258	5.984	0.035	0.139	6	6 1/4	1/8
259	6.234	0.040	0.139	6 1/4	6 1/2	1/8
260	6.484	0.040	0.139	6 1/2	6 3/4	1/8
261	6.734	0.040	0.139	6 3/4	7	1/8
262	6.984	0.040	0.139	7	7 1/4	1/8
263	7.234	0.045	0.139	7 1/4	7 1/2	1/8
264	7.484	0.045	0.139	7 1/2	7 3/4	1/8
265	7.734	0.045	0.139	7 3/4	8	1/8
266	7.984	0.045	0.139	8	8 1/4	1/8
267	8.234	0.050	0.139	8 1/4	8 1/2	1/8
268	8.484	0.050	0.139	8 1/2	8 3/4	1/8
269	8.734	0.050	0.139	8 3/4	9	1/8
270	8.984	0.050	0.139	9	9 1/4	1/8
271	9.234	0.055	0.139	9 1/4	9 1/2	1/8
272	9.484	0.055	0.139	9 1/2	9 3/4	1/8
273	9.734	0.055	0.139	9 3/4	10	1/8
274	9.984	0.055	0.139	10	10 1/4	1/8
275	10.484	0.055	0.139	10 1/2	10 3/4	1/8
276	10.984	0.065	0.139	11	11 1/4	1/8
277	11.484	0.065	0.139	11 1/2	11 3/4	1/8
278	11.984	0.065	0.139	12	12 1/4	1/8
279	12.984	0.065	0.139	13	13 1/4	1/8
280	13.984	0.065	0.139	14	14 1/4	1/8
281	14.984	0.065	0.139	15	15 1/4	1/8
282	15.955	0.075	0.139	16	16 1/4	1/8
283	16.955	0.080	0.139	17	17 1/4	1/8
284	17.955	0.085	0.139	18	18 1/4	1/8

**Table 4. O-Ring Size Chart for 300 Series.** AS568A designation, actual size and nominal size. Dimensions are in inches. (Note: Nominal size is approximate and for reference only.)
O-Ring Size Chart 4
300 Series Cross Section: 3/16" (0.210" ±0.005")
AS568A Dash Number	Actual Size			Nominal Size
AS568A Dash Number	ID	ID ±	CS	ID	OD	CS
309	0.412	0.005	0.210	7/16	13/16	3/16
310	0.475	0.005	0.210	1/2	7/8	3/16
311	0.537	0.007	0.210	9/16	15/16	3/16
312	0.600	0.009	0.210	5/8	1	3/16
313	0.662	0.009	0.210	11/16	1 1/16	3/16
314	0.725	0.010	0.210	3/4	1 1/8	3/16
315	0.787	0.010	0.210	13/16	1 3/16	3/16
316	0.850	0.010	0.210	7/8	1 1/4	3/16
317	0.912	0.010	0.210	15/16	1 5/16	3/16
318	0.975	0.010	0.210	1	1 3/8	3/16
319	1.037	0.010	0.210	1 1/16	1 7/16	3/16
320	1.100	0.012	0.210	1 1/8	1 1/2	3/16
321	1.162	0.012	0.210	1 3/16	1 9/16	3/16
322	1.225	0.012	0.210	1 1/4	1 5/8	3/16
323	1.287	0.012	0.210	1 5/16	1 11/16	3/16
324	1.350	0.012	0.210	1 3/8	1 3/4	3/16
325	1.475	0.015	0.210	1 1/2	1 7/8	3/16
326	1.600	0.015	0.210	1 5/8	2	3/16
327	1.725	0.015	0.210	1 3/4	2 1/8	3/16
328	1.850	0.015	0.210	1 7/8	2 1/4	3/16
329	1.975	0.018	0.210	2	2 3/8	3/16
330	2.100	0.018	0.210	2 1/8	2 1/2	3/16
331	2.225	0.018	0.210	2 1/4	2 5/8	3/16
332	2.350	0.018	0.210	2 3/8	2 3/4	3/16
333	2.475	0.020	0.210	2 1/2	2 7/8	3/16
334	2.600	0.020	0.210	2 5/8	3	3/16
335	2.725	0.020	0.210	2 3/4	3 1/8	3/16
336	2.850	0.020	0.210	2 7/8	3 1/4	3/16
337	2.975	0.024	0.210	3	3 3/8	3/16
338	3.100	0.024	0.210	3 1/8	3 1/2	3/16
339	3.225	0.024	0.210	3 1/4	3 5/8	3/16
340	3.350	0.024	0.210	3 3/8	3 3/4	3/16
341	3.475	0.024	0.210	3 1/2	3 7/8	3/16
342	3.600	0.028	0.210	3 5/8	4	3/16
343	3.725	0.028	0.210	3 3/4	4 1/8	3/16
344	3.850	0.028	0.210	3 7/8	4 1/4	3/16
345	3.975	0.028	0.210	4	4 3/8	3/16
346	4.100	0.028	0.210	4 1/8	4 1/2	3/16
347	4.225	0.030	0.210	4 1/4	4 5/8	3/16
348	4.350	0.030	0.210	4 3/8	4 3/4	3/16
349	4.475	0.030	0.210	4 1/2	4 7/8	3/16
350	4.600	0.030	0.210	4 5/8	5	3/16
351	4.725	0.030	0.210	4 3/4	5 1/8	3/16
352	4.850	0.030	0.210	4 7/8	5 1/4	3/16
353	4.975	0.037	0.210	5	5 3/8	3/16
354	5.100	0.037	0.210	5 1/8	5 1/2	3/16
355	5.225	0.037	0.210	5 1/4	5 5/8	3/16
356	5.350	0.037	0.210	5 3/8	5 3/4	3/16
357	5.475	0.037	0.210	5 1/2	5 7/8	3/16
358	5.600	0.037	0.210	5 5/8	6	3/16
359	5.725	0.037	0.210	5 3/4	6 1/8	3/16
360	5.850	0.037	0.210	5 7/8	6 1/4	3/16
361	5.975	0.037	0.210	6	6 3/8	3/16
362	6.225	0.040	0.210	6 1/4	6 5/8	3/16
363	6.475	0.040	0.210	6 1/2	6 7/8	3/16
364	6.725	0.040	0.210	6 3/4	7 1/8	3/16
365	6.975	0.040	0.210	7	7 3/8	3/16
366	7.225	0.045	0.210	7 1/4	7 5/8	3/16
367	7.475	0.045	0.210	7 1/2	7 7/8	3/16
368	7.725	0.045	0.210	7 3/4	8 1/8	3/16
369	7.975	0.045	0.210	8	8 3/8	3/16
370	8.225	0.050	0.210	8 1/4	8 5/8	3/16
371	8.475	0.050	0.210	8 1/2	8 7/8	3/16
372	8.725	0.050	0.210	8 3/4	9 1/8	3/16
373	8.975	0.050	0.210	9	9 3/8	3/16
374	9.225	0.055	0.210	9 1/4	9 5/8	3/16
375	9.475	0.055	0.210	9 1/2	9 7/8	3/16
376	9.725	0.055	0.210	9 3/4	10 1/8	3/16
377	9.975	0.055	0.210	10	10 3/8	3/16
378	10.475	0.060	0.210	10 1/2	10 7/8	3/16
379	10.975	0.060	0.210	11	11 3/8	3/16
380	11.475	0.065	0.210	11 1/2	11 7/8	3/16
381	11.975	0.065	0.210	12	12 3/8	3/16
382	12.975	0.065	0.210	13	13 3/8	3/16
383	13.975	0.070	0.210	14	14 3/8	3/16
384	14.975	0.070	0.210	15	15 3/8	3/16
385	15.955	0.075	0.210	16	16 3/8	3/16
386	16.955	0.080	0.210	17	17 3/8	3/16
387	17.955	0.085	0.210	18	18 3/8	3/16
388	18.955	0.090	0.210	19	19 3/8	3/16
389	19.955	0.095	0.210	20	20 3/8	3/16
390	20.955	0.095	0.210	21	21 3/8	3/16
391	21.955	0.100	0.210	22	22 3/8	3/16
392	22.940	0.105	0.210	23	23 3/8	3/16
393	23.940	0.110	0.210	24	24 3/8	3/16
394	24.940	0.115	0.210	25	25 3/8	3/16
395	25.940	0.120	0.210	26	26 3/8	3/16

**Table 5. O-Ring Size Chart for 400 Series.** AS568A designation, actual size and nominal size. Dimensions are in inches. (Note: Nominal size is approximate and for reference only.)
O-Ring Size Chart 5
400 Series Cross Section: 1/4" (0.275" ±0.006")
AS568A Dash Number	Actual Size			Nominal Size
AS568A Dash Number	ID	ID ±	CS	ID	OD	CS
425	4.475	0.033	0.275	4 1/2	5	1/4
426	4.600	0.033	0.275	4 5/8	5 1/8	1/4
427	4.725	0.033	0.275	4 3/4	5 1/4	1/4
428	4.850	0.033	0.275	4 7/8	5 3/8	1/4
429	4.975	0.037	0.275	5	5 1/2	1/4
430	5.100	0.037	0.275	5 1/8	5 5/8	1/4
431	5.225	0.037	0.275	5 1/4	5 3/4	1/4
432	5.350	0.037	0.275	5 3/8	5 7/8	1/4
433	5.475	0.037	0.275	5 1/2	6	1/4
434	5.600	0.037	0.275	5 5/8	6 1/8	1/4
435	5.725	0.037	0.275	5 3/4	6 1/4	1/4
436	5.850	0.037	0.275	5 7/8	6 3/8	1/4
437	5.975	0.037	0.275	6	6 1/2	1/4
438	6.225	0.040	0.275	6 1/4	6 3/4	1/4
439	6.475	0.040	0.275	6 1/2	7	1/4
440	6.725	0.040	0.275	6 3/4	7 1/4	1/4
441	6.975	0.040	0.275	7	7 1/2	1/4
442	7.225	0.045	0.275	7 1/4	7 3/4	1/4
443	7.475	0.045	0.275	7 1/2	8	1/4
444	7.725	0.045	0.275	7 3/4	8 1/4	1/4
445	7.975	0.045	0.275	8	8 1/2	1/4
446	8.475	0.055	0.275	8 1/2	9	1/4
447	8.975	0.055	0.275	9	9 1/2	1/4
448	9.475	0.055	0.275	9 1/2	10	1/4
449	9.975	0.055	0.275	10	10 1/2	1/4
450	10.475	0.060	0.275	10 1/2	11	1/4
451	10.975	0.060	0.275	11	11 1/2	1/4
452	11.475	0.060	0.275	11 1/2	12	1/4
453	11.975	0.060	0.275	12	12 1/2	1/4
454	12.475	0.060	0.275	12 1/2	13	1/4
455	12.975	0.060	0.275	13	13 1/2	1/4
456	13.475	0.070	0.275	13 1/2	14	1/4
457	13.975	0.070	0.275	14	14 1/2	1/4
458	14.475	0.070	0.275	14 1/2	15	1/4
459	14.975	0.070	0.275	15	15 1/2	1/4
460	15.475	0.070	0.275	15 1/2	16	1/4
461	15.955	0.075	0.275	16	16 1/2	1/4
462	16.455	0.075	0.275	16 1/2	17	1/4
463	16.955	0.080	0.275	17	17 1/2	1/4
464	17.455	0.085	0.275	17 1/2	18	1/4
465	17.955	0.085	0.275	18	18 1/2	1/4
466	18.455	0.085	0.275	18 1/2	19	1/4
467	18.955	0.090	0.275	19	19 1/2	1/4
468	19.455	0.090	0.275	19 1/2	20	1/4
469	19.955	0.095	0.275	20	20 1/2	1/4
470	20.955	0.095	0.275	21	21 1/2	1/4
471	21.955	0.100	0.275	22	22 1/2	1/4
472	22.940	0.105	0.275	23	23 1/2	1/4
473	23.940	0.110	0.275	24	24 1/2	1/4
474	24.940	0.115	0.275	25	25 1/2	1/4
475	25.940	0.120	0.275	26	26 1/2	1/4

**Table 6. O-Ring Material Physical Properties.** Comparison of physical properties of Buna-N and Viton® materials. (Note: Ratings are a general guideline only.)
O-Ring Material Physical Properties
Property	Buna-N	Viton®
Tensile Strength	Good	Good
Elongation	Good	Fair
Low Temperature Flexibility	Good	Poor
Compression Set	Good	Excellent
Tear Resistance	Good	Fair
Abrasion Resistance	Excellent	Good
Flame Resistance	Poor	Excellent
Gas Permeability	Good	Excellent

**Table 7. O-Ring Material Chemical Resistance.** Comparison of chemical resistance of Buna-N and Viton® materials. (Note: Ratings are a general guideline only.)
O-Ring Material Chemical Resistance
Chemical	Resistance
Chemical	Buna-N	Viton®
Anhydrous Ammonia	-	Poor
Brake Fluid	Poor	-
Dilute Acids	Good	Excellent
Dilute Alkalis	Good	Excellent
Hydraulic Fluids	Good	-
Ketones	Poor	Fair
Ozone	Poor	Excellent
Petroleum Oil(s)	Excellent	Excellent
Silicone Lubricants	Excellent	-
Solvents	-	Excellent
Steam	Fair	Fair
Strong Acids	Poor	-
Transmission Fluid	Good	-
Water	Excellent	Excellent
Weather	Poor	Excellent

CI:ORNGS v1.1

O-RINGS

Buna-N

Viton®

O-Ring Size Chart 1

O-Ring Size Chart 2

O-Ring Size Chart 3

O-Ring Size Chart 4

O-Ring Size Chart 5

O-Ring Material Physical Properties

O-Ring Material Chemical Resistance