As the poster above mentioned, SAR-1s never had a threaded muzzle. They were imported from 2000-2004 during the ban when such things were verboten. Some however have the muzzle threaded by a gunsmith.
The SAR-1 is probably my favorite AK, and I've had several ranging from a Hungarian SA-85, a couple of Polish Underfolders, Romy G-Kits, and Yugos. I got rid of them all except my SAR-1 and a Yugo. One of the best things about the SAR-1 is how close it is to an original Romanian Military AK. It has a cold hammer forged Romanian barrel and the receiver is Cugir Arsenal made, not an American reverse engineered copy.
Only thing I'd recommend on an SAR-1 is to pull the FCG out and replace it. The US compliance FCG Century used tends to have trigger slap. It is an cheap and easily replaced part, and removes one of the only big issues on the SAR-1. I used a Tapco G2...