Our Leather Seal Replacement threads direct into the piston. The thread is commonly an 5m x 1m in most Leather Seal attachments. If the thread is different from the one we supply, the OEM screw that is currently in the Leather Seal may be put through the hole of the seal retainer and used. Either way, there is now an option to use synthetic sealing to greatly improve shot cycle and velocity performance. Vortek Vac-Seal 25 adapter, also includes a Vac-Seal 25 piston seal. For older Weihrauch HW30, 50, 55, Diana 25 and 27, and Gamo models with leather piston seal in 25mm. Vortek developed this adapter for the ability to convert old air guns with leather piston seal, to synthetic seal. This adapter / upgrade is designed primarily for 25mm cylinder Gamo models and Weihrauch HW30, 50, 55 with leather piston seal mounted. With this upgrade to VORTEK Vac-Seal 25 synthetic piston seal, you obtain significantly better performance and smoother operation, and significantly more damping against piston slam. Easily installed with a standard Allen key. VORTEK Vac-Seal also prevents spring fracture, which is commonly found on older spring rifles with leather piston seal. Fits directly without modifications on following spring air rifles: Weihrauch HW30, HW50, HW55 (old model with leather piston seal.) Gamo 300, 361, 400, 45-s-61, 600c, 68, Cadet, Expo, Expomatic, Gamatic, Stamic, Statical, Sniper. (With screwed leather piston seal) Diana 25 and 27 models. Falke 60 Extended compatibility list of the models that are suitable for Vac-Seal 25 conversion, will be added.