Commercial Model 1917's made after about 1926 do have hammer blocks; the original U.S. M1917 does not. My Brazilian contract gun does not, but I understand some do. Anyway, that is why there are two sideplates listed for the 1917. The hammer block is p/n 53 in that diagram; it is the second S&W type, introduced c. 1926, not the current type.
Guns made for that type of hammer block have a slot in the sideplate and a hand with a sloped ramp that pushes the hammer block back into the sideplate when the trigger is pulled (not up and down as in the current system). You should be able to see the hammer block in your gun (if it is there) if you use a strong light and look into the hammer slot as you cock the hammer.
Last edited by James K; June 16, 2010 at 09:10 PM.