One of the most common questions posted on airgun forums is "what size o-ring do I need for this"? Many of the PCP manufacturers don't publish schematics or parts lists with o-ring sizes because they either want the income from parts and service sales or they just don't want people to work on their own PCPs.
A digital caliper is amust have tool for all PCP, compressor, and tank owners. A digital caliper and an o-ring size chart are all that's needed to size an o-ring and then cross reference it to size an o-ring. All metric o-rings are numbered by their thickness and inner diameter in millimeters. Many common metric sizes even cross reference to USA standard sizes which have an A prefix. For instance, a 1.5 x 5 metric o-ring has a 1.5mm thickness and an inner diameter of 5mm and an outer diameter of 8mm. The outer diameter is the inner diameter plus double the thickness of the o-ring. In this instance a 5mm inner diameter plus 1.5 thickness x 2 = 8mm. There are many commonly used o-rings that can be found in USA standard and metric o-ring kits. Most o-rings used in PCPs are 70 durometer buna, with a few that are 90 durometer. The higher durometer number refers to the hardness for higher wear such as on pellet probes or barrel breach seals.
All of this may sound confusing at first, but with a little research and willingness to learn, an owner can save themselves lots of time and expense by resealing their own PCPs, fittings, and tanks. I use a digital caliper to find the exact size of many parts and accessories in and outside of airgunning.
Here is an o-ring chart I have referenced many times. A digital caliper can cost as little as $10. It is a must have tool if you want to be independent and reseal your own equipment.
https://www.marcorubber.com/o-ring-size-chart-as568.htm
A digital caliper is amust have tool for all PCP, compressor, and tank owners. A digital caliper and an o-ring size chart are all that's needed to size an o-ring and then cross reference it to size an o-ring. All metric o-rings are numbered by their thickness and inner diameter in millimeters. Many common metric sizes even cross reference to USA standard sizes which have an A prefix. For instance, a 1.5 x 5 metric o-ring has a 1.5mm thickness and an inner diameter of 5mm and an outer diameter of 8mm. The outer diameter is the inner diameter plus double the thickness of the o-ring. In this instance a 5mm inner diameter plus 1.5 thickness x 2 = 8mm. There are many commonly used o-rings that can be found in USA standard and metric o-ring kits. Most o-rings used in PCPs are 70 durometer buna, with a few that are 90 durometer. The higher durometer number refers to the hardness for higher wear such as on pellet probes or barrel breach seals.
All of this may sound confusing at first, but with a little research and willingness to learn, an owner can save themselves lots of time and expense by resealing their own PCPs, fittings, and tanks. I use a digital caliper to find the exact size of many parts and accessories in and outside of airgunning.
Here is an o-ring chart I have referenced many times. A digital caliper can cost as little as $10. It is a must have tool if you want to be independent and reseal your own equipment.
https://www.marcorubber.com/o-ring-size-chart-as568.htm
