RE: Welcome to Club SAITO !
Gentleman,
I just wrote a note to Brenton (who by the way runs an incredible web site) with the following information.
The muffler thread size on the production run 125a engines is 13 x 1mm. The original preproduction protoypes had the 1/2 - 20 threads but that size did not make it to production.
Pete
Radio & Engine Category Manager
Horizon Hobby Inc.