There are 2 sizes, mine is the larger @ 115mm, the smaller size is 90mm.
http://www.apexi-usa.com/products/?id=5327
"The ATS was developed as a high performance evolution to the standard tail pipe silencers available in the market today. While many people enjoy the power gains of a racing exhaust on the track, often times these systems require a silencer to be installed in the tip for use on the street. While sound output can be dramatically lowered using a non-adjustable silencer, unfortunately response and power tend to suffer due to increased exhaust gas restriction. The ATS (Active Tail Silencer) uses the same active valve technology as the PS Revolution exhaust system. The spring loaded valve is engaged and disengaged based upon exhaust gas pressure. This allows for effective sound suppression for the street, without the power loss under high load. Dyno tests have proven power levels to be nearly identical to an exhaust using no silencer at all. * Please note that, due to the tapered tip of the N1 Evolution exhaust system the ATS Silencer WILL NOT fit properly. This is only true for the N1 EVOLUTION mufflers, all other"