Requirements for Choke Installation In order to install choke tubes in your barrel, the barrel must meet the the following minimum and maximum dimensions. If you have access to a caliper you can check it on your end. If not, you can just send the barrel and I can check it on my end. Terminology...Outside Diameter (OD) .............Inside Diameter (ID) Minimum OD at the muzzle for 12 ga. Standard Diameter Truchoke style tube installation: .825" Minimum OD at the muzzle for 12 ga. Thinwall Truchoke style tube installation: .805" Maximum ID of the bore for 12 ga. Standard Diameter Truchoke style tube installation: .735" Maximum ID of the bore for 12 ga. Thinwall Truchoke style tube installation: .728" Minimum OD at the muzzle for 20 ga. Standard Diameter Truchoke style tube installation: .705" Maximum ID of the bore for 20 ga. Standard Diameter Truchoke style tube installation: .625" For any questions or other info please email or call. If you leave a message I will return your call. Visit my Contact Info page for contact information and shipping instructions. Home