O-Ring Size Chart and Gland Dimensions
AS568 standard O-ring sizes by dash number in inches and millimetres, the five standard cross-sections, and worked gland dimensions (depth, groove width, squeeze and clearance) for static radial, dynamic radial and face seals.
AS568 cross-sections
| Series | Starts at | Nominal (in) | Actual (in) | Tolerance (in) | Actual (mm) |
|---|---|---|---|---|---|
| -0xx | -004 | 1/16 | 0.070 | ±0.003 | 1.78 |
| -1xx | -102 | 3/32 | 0.103 | ±0.003 | 2.62 |
| -2xx | -201 | 1/8 | 0.139 | ±0.004 | 3.53 |
| -3xx | -309 | 3/16 | 0.210 | ±0.005 | 5.33 |
| -4xx | -425 | 1/4 | 0.275 | ±0.006 | 6.99 |
Dash numbers -001 to -003 use smaller special sections and are not listed. ISO 3601 metric sections for comparison: 1.80, 2.65, 3.55, 5.30, 7.00 mm.
AS568 size chart
Nominal sizes for every even dash number from -008 to -050, -110 to -150 and -210 to -250, and every size from -325 to -350. OD is ID plus two sections. Millimetres are converted from inches.
| Dash no. | ID (in) | CS (in) | OD (in) | ID (mm) | CS (mm) |
|---|---|---|---|---|---|
| -0xx series, 0.070 in (1.78 mm) section | |||||
| -008 | 0.176 | 0.070 | 0.316 | 4.47 | 1.78 |
| -010 | 0.239 | 0.070 | 0.379 | 6.07 | 1.78 |
| -012 | 0.364 | 0.070 | 0.504 | 9.25 | 1.78 |
| -014 | 0.489 | 0.070 | 0.629 | 12.42 | 1.78 |
| -016 | 0.614 | 0.070 | 0.754 | 15.60 | 1.78 |
| -018 | 0.739 | 0.070 | 0.879 | 18.77 | 1.78 |
| -020 | 0.864 | 0.070 | 1.004 | 21.95 | 1.78 |
| -022 | 0.989 | 0.070 | 1.129 | 25.12 | 1.78 |
| -024 | 1.114 | 0.070 | 1.254 | 28.30 | 1.78 |
| -026 | 1.239 | 0.070 | 1.379 | 31.47 | 1.78 |
| -028 | 1.364 | 0.070 | 1.504 | 34.65 | 1.78 |
| -030 | 1.614 | 0.070 | 1.754 | 41.00 | 1.78 |
| -032 | 1.864 | 0.070 | 2.004 | 47.35 | 1.78 |
| -034 | 2.114 | 0.070 | 2.254 | 53.70 | 1.78 |
| -036 | 2.364 | 0.070 | 2.504 | 60.05 | 1.78 |
| -038 | 2.614 | 0.070 | 2.754 | 66.40 | 1.78 |
| -040 | 2.864 | 0.070 | 3.004 | 72.75 | 1.78 |
| -042 | 3.239 | 0.070 | 3.379 | 82.27 | 1.78 |
| -044 | 3.739 | 0.070 | 3.879 | 94.97 | 1.78 |
| -046 | 4.239 | 0.070 | 4.379 | 107.67 | 1.78 |
| -048 | 4.739 | 0.070 | 4.879 | 120.37 | 1.78 |
| -050 | 5.239 | 0.070 | 5.379 | 133.07 | 1.78 |
| -1xx series, 0.103 in (2.62 mm) section | |||||
| -110 | 0.362 | 0.103 | 0.568 | 9.19 | 2.62 |
| -112 | 0.487 | 0.103 | 0.693 | 12.37 | 2.62 |
| -114 | 0.612 | 0.103 | 0.818 | 15.54 | 2.62 |
| -116 | 0.737 | 0.103 | 0.943 | 18.72 | 2.62 |
| -118 | 0.862 | 0.103 | 1.068 | 21.89 | 2.62 |
| -120 | 0.987 | 0.103 | 1.193 | 25.07 | 2.62 |
| -122 | 1.112 | 0.103 | 1.318 | 28.24 | 2.62 |
| -124 | 1.237 | 0.103 | 1.443 | 31.42 | 2.62 |
| -126 | 1.362 | 0.103 | 1.568 | 34.59 | 2.62 |
| -128 | 1.487 | 0.103 | 1.693 | 37.77 | 2.62 |
| -130 | 1.612 | 0.103 | 1.818 | 40.94 | 2.62 |
| -132 | 1.737 | 0.103 | 1.943 | 44.12 | 2.62 |
| -134 | 1.862 | 0.103 | 2.068 | 47.29 | 2.62 |
| -136 | 1.987 | 0.103 | 2.193 | 50.47 | 2.62 |
| -138 | 2.112 | 0.103 | 2.318 | 53.64 | 2.62 |
| -140 | 2.237 | 0.103 | 2.443 | 56.82 | 2.62 |
| -142 | 2.362 | 0.103 | 2.568 | 59.99 | 2.62 |
| -144 | 2.487 | 0.103 | 2.693 | 63.17 | 2.62 |
| -146 | 2.612 | 0.103 | 2.818 | 66.34 | 2.62 |
| -148 | 2.737 | 0.103 | 2.943 | 69.52 | 2.62 |
| -150 | 2.862 | 0.103 | 3.068 | 72.69 | 2.62 |
| -2xx series, 0.139 in (3.53 mm) section | |||||
| -210 | 0.734 | 0.139 | 1.012 | 18.64 | 3.53 |
| -212 | 0.859 | 0.139 | 1.137 | 21.82 | 3.53 |
| -214 | 0.984 | 0.139 | 1.262 | 24.99 | 3.53 |
| -216 | 1.109 | 0.139 | 1.387 | 28.17 | 3.53 |
| -218 | 1.234 | 0.139 | 1.512 | 31.34 | 3.53 |
| -220 | 1.359 | 0.139 | 1.637 | 34.52 | 3.53 |
| -222 | 1.484 | 0.139 | 1.762 | 37.69 | 3.53 |
| -224 | 1.734 | 0.139 | 2.012 | 44.04 | 3.53 |
| -226 | 1.984 | 0.139 | 2.262 | 50.39 | 3.53 |
| -228 | 2.234 | 0.139 | 2.512 | 56.74 | 3.53 |
| -230 | 2.484 | 0.139 | 2.762 | 63.09 | 3.53 |
| -232 | 2.734 | 0.139 | 3.012 | 69.44 | 3.53 |
| -234 | 2.984 | 0.139 | 3.262 | 75.79 | 3.53 |
| -236 | 3.234 | 0.139 | 3.512 | 82.14 | 3.53 |
| -238 | 3.484 | 0.139 | 3.762 | 88.49 | 3.53 |
| -240 | 3.734 | 0.139 | 4.012 | 94.84 | 3.53 |
| -242 | 3.984 | 0.139 | 4.262 | 101.19 | 3.53 |
| -244 | 4.234 | 0.139 | 4.512 | 107.54 | 3.53 |
| -246 | 4.484 | 0.139 | 4.762 | 113.89 | 3.53 |
| -248 | 4.734 | 0.139 | 5.012 | 120.24 | 3.53 |
| -250 | 4.984 | 0.139 | 5.262 | 126.59 | 3.53 |
| -3xx series, 0.210 in (5.33 mm) section | |||||
| -325 | 1.475 | 0.210 | 1.895 | 37.47 | 5.33 |
| -326 | 1.600 | 0.210 | 2.020 | 40.64 | 5.33 |
| -327 | 1.725 | 0.210 | 2.145 | 43.82 | 5.33 |
| -328 | 1.850 | 0.210 | 2.270 | 46.99 | 5.33 |
| -329 | 1.975 | 0.210 | 2.395 | 50.17 | 5.33 |
| -330 | 2.100 | 0.210 | 2.520 | 53.34 | 5.33 |
| -331 | 2.225 | 0.210 | 2.645 | 56.52 | 5.33 |
| -332 | 2.350 | 0.210 | 2.770 | 59.69 | 5.33 |
| -333 | 2.475 | 0.210 | 2.895 | 62.87 | 5.33 |
| -334 | 2.600 | 0.210 | 3.020 | 66.04 | 5.33 |
| -335 | 2.725 | 0.210 | 3.145 | 69.22 | 5.33 |
| -336 | 2.850 | 0.210 | 3.270 | 72.39 | 5.33 |
| -337 | 2.975 | 0.210 | 3.395 | 75.57 | 5.33 |
| -338 | 3.100 | 0.210 | 3.520 | 78.74 | 5.33 |
| -339 | 3.225 | 0.210 | 3.645 | 81.91 | 5.33 |
| -340 | 3.350 | 0.210 | 3.770 | 85.09 | 5.33 |
| -341 | 3.475 | 0.210 | 3.895 | 88.27 | 5.33 |
| -342 | 3.600 | 0.210 | 4.020 | 91.44 | 5.33 |
| -343 | 3.725 | 0.210 | 4.145 | 94.62 | 5.33 |
| -344 | 3.850 | 0.210 | 4.270 | 97.79 | 5.33 |
| -345 | 3.975 | 0.210 | 4.395 | 100.97 | 5.33 |
| -346 | 4.100 | 0.210 | 4.520 | 104.14 | 5.33 |
| -347 | 4.225 | 0.210 | 4.645 | 107.31 | 5.33 |
| -348 | 4.350 | 0.210 | 4.770 | 110.49 | 5.33 |
| -349 | 4.475 | 0.210 | 4.895 | 113.66 | 5.33 |
| -350 | 4.600 | 0.210 | 5.020 | 116.84 | 5.33 |
Nominal dimensions. ID tolerances grow with size; confirm the exact ID and tolerance against the current AS568 revision or your seal supplier's size table.
Need seal grooves turned or milled to print? .
Gland design guidance
General starting points, worked from our own rule set rather than any vendor table: a target squeeze per seal type (lighter for dynamic, heavier for face seals, higher percentage on small sections), a turnable depth band, and a groove width that keeps the ring at or under 75% of the groove area at worst case. The squeeze column is the worst case across the section tolerance and the depth band. Widths are for glands without backup rings. Confirm any production gland with your seal supplier's design guide for the compound, pressure, temperature and fluid.
Static radial (piston or rod, no motion)
| Series | Gland depth (in) | Groove width (in) | Squeeze | Diametral clearance (in) |
|---|---|---|---|---|
| -0xx0.070 in CS | 0.052 to 0.0541.32 to 1.37 mm | 0.108 to 0.1132.74 to 2.87 mm | 19.4 to 28.8% | 0.002 to 0.005 |
| -1xx0.103 in CS | 0.079 to 0.0812.01 to 2.06 mm | 0.149 to 0.1543.78 to 3.91 mm | 19.0 to 25.5% | 0.002 to 0.005 |
| -2xx0.139 in CS | 0.110 to 0.1122.79 to 2.84 mm | 0.195 to 0.2004.95 to 5.08 mm | 17.0 to 23.1% | 0.003 to 0.006 |
| -3xx0.210 in CS | 0.170 to 0.1744.32 to 4.42 mm | 0.285 to 0.2907.24 to 7.37 mm | 15.1 to 20.9% | 0.003 to 0.006 |
| -4xx0.275 in CS | 0.224 to 0.2285.69 to 5.79 mm | 0.370 to 0.3759.40 to 9.52 mm | 15.2 to 20.3% | 0.004 to 0.007 |
Dynamic radial (reciprocating piston or rod)
| Series | Gland depth (in) | Groove width (in) | Squeeze | Diametral clearance (in) |
|---|---|---|---|---|
| -0xx0.070 in CS | 0.058 to 0.0601.47 to 1.52 mm | 0.097 to 0.1022.46 to 2.59 mm | 10.4 to 20.5% | 0.002 to 0.005 |
| -1xx0.103 in CS | 0.087 to 0.0892.21 to 2.26 mm | 0.136 to 0.1413.45 to 3.58 mm | 11.0 to 17.9% | 0.002 to 0.005 |
| -2xx0.139 in CS | 0.119 to 0.1213.02 to 3.07 mm | 0.180 to 0.1854.57 to 4.70 mm | 10.4 to 16.8% | 0.003 to 0.006 |
| -3xx0.210 in CS | 0.179 to 0.1834.55 to 4.65 mm | 0.271 to 0.2766.88 to 7.01 mm | 10.7 to 16.7% | 0.003 to 0.006 |
| -4xx0.275 in CS | 0.235 to 0.2395.97 to 6.07 mm | 0.352 to 0.3578.94 to 9.07 mm | 11.2 to 16.4% | 0.004 to 0.007 |
Static face (axial, flange or cover)
| Series | Gland depth (in) | Groove width (in) | Squeeze | Diametral clearance (in) |
|---|---|---|---|---|
| -0xx0.070 in CS | 0.051 to 0.0531.30 to 1.35 mm | 0.110 to 0.1152.79 to 2.92 mm | 20.9 to 30.1% | None: faces clamp metal to metal |
| -1xx0.103 in CS | 0.075 to 0.0771.90 to 1.96 mm | 0.157 to 0.1623.99 to 4.11 mm | 23.0 to 29.2% | None: faces clamp metal to metal |
| -2xx0.139 in CS | 0.103 to 0.1052.62 to 2.67 mm | 0.208 to 0.2135.28 to 5.41 mm | 22.2 to 28.0% | None: faces clamp metal to metal |
| -3xx0.210 in CS | 0.158 to 0.1624.01 to 4.11 mm | 0.307 to 0.3127.80 to 7.92 mm | 21.0 to 26.5% | None: faces clamp metal to metal |
| -4xx0.275 in CS | 0.207 to 0.2115.26 to 5.36 mm | 0.400 to 0.40510.16 to 10.29 mm | 21.6 to 26.3% | None: faces clamp metal to metal |
Design notes
- Gland depth is measured from the groove bottom to the mating bore or rod with the parts concentric, so it includes half the diametral clearance. Side load or eccentricity takes squeeze from one side and adds it to the other.
- Piston seals: pick the ring whose ID is just under the groove diameter, so it stretches about 1 to 5% when installed. Much more than 5% thins the section and eats into squeeze.
- Face seals under internal pressure should sit against the outer groove wall (groove OD about equal to ring OD); under external pressure, against the inner wall.
- Above roughly 1,500 psi, or where the clearance is at the top of its range, add a backup ring (PTFE or hard nylon) on the low-pressure side and widen the groove by its thickness.
- Surface finish: about 32 µin Ra (0.8 µm) or better on static sealing surfaces, finer for gas; 8 to 16 µin Ra (0.2 to 0.4 µm) on the sliding surface of a dynamic seal.
- Break the edges the ring slides over with a 15 to 20 degree lead-in chamfer, radius the groove corners, and keep threads and cross holes out of its path during assembly.
Frequently asked questions
- What do AS568 dash numbers mean?
- The first digit gives the cross-section series and the rest counts up through the inside diameters. Every -2xx ring has a 0.139 in section, and -214 is 0.984 in ID by 0.139 in. Within a series a higher number means a larger ID.
- How much squeeze does an O-ring need?
- As a rough guide: about 10 to 20% for reciprocating dynamic seals, 15 to 30% for static radial seals and 20 to 30% for face seals, with small sections toward the top of each range because their absolute squeeze is tiny. The worked glands on this page stay inside their bands at the tolerance extremes, except where the section tolerance is too large a share of a small section to hold the band with a depth specified to three decimals: the dynamic -0xx gland runs 10.4 to 20.5% and the face -0xx gland runs 20.9 to 30.1%.
- Can I use a metric O-ring in an AS568 gland?
- Often, but check it. The common ISO 3601 metric sections (1.80, 2.65, 3.55, 5.30 and 7.00 mm) sit within a few hundredths of a millimetre of the AS568 sections (1.78, 2.62, 3.53, 5.33 and 6.99 mm). Recheck squeeze and gland fill at the tolerance extremes and the stretch on the ID before you swap.
- What is gland fill and why leave room?
- Gland fill is the share of the groove cross-section the squeezed ring occupies. The ring swells in many fluids and expands with heat faster than the metal around it, so it needs somewhere to go. A ring that fills the groove solid is forced into the clearance gap and extrudes. We size groove widths for no more than 75% fill at worst case.
- Which O-ring material should I use?
- Nitrile (NBR, Buna-N) is the general default for petroleum oils, hydraulic fluid and water. FKM (Viton) handles higher temperatures and fuels. EPDM suits water, steam and brake fluid but swells in petroleum oils. Silicone covers a wide temperature range in static seals. 70 Shore A is the usual hardness; 90 Shore A resists extrusion at high pressure.
