Mec-Gar Sig Sauer SCT style P228 or P229 18 round 9mm magazine with the anti-friction coating. This magazine is compatible with the Sig Sauer P229 9mm with the narrow tube magazines but not the newer P229-1 or P229 E2 style pistols that use the same width magazine as the P229 .40 S&W/.357 Sig.
The Sig Sauer P229 E2 9mm and Sig P229 made from late December 2010 now has a wider magwell which is the same a the Sig Sauer P229 .40/.357. For those pistols you need to use a Sig Sauer P229-1 magazine. While these will lock in to place they will have some play in the magwell that may cause reliability issues. These magazines are for the P228 or P229 9mm that have the narrower magwell.