I believe it is a carbon steel version of the 4006. The 4003 is the alloy framed version. I own a 4003TSW, a 5903TSW, and a 5943TSW. All three have an alloy frame. The above mentioned pistol would be a 4026 if it had a frame mounted decocker and a stainless frame. I have never heard of S & W making an alloy framed frame mounted decocker pistol. However, it wouldn't be the first time I have been proven wrong.