Model 1911

Note 1: Most Springfields have a "s" stamped on inside flat. Note the checkering extends up high.
Note 2: All M1911 slide stops have the relief cut under the curve and all M1911A1s lack the cut.

Note 1: Colt started using serrated slide stop on late 1,600,000 range. That would put it around October 1944. But, then again, you see either/or around this serial range.
Note 2: In the 1911A1 826xxx range an unknown number of pistols seem to have the slide stop with the relief under the rear thumb ledge. This feature was supposed to be ended with the transition pistols (700001 through 710000). The earlier slide stop was observed on multiple pistols in the  826xxx range. Apparently Colts found a batch of the older parts and decided to use them up. The range of serial numbers that this older slide stop covers is at this point unknown and needs further observation.

Note 1: Serrated slide stops observed on Ithacas as early as the 1,200,000 range.
Note 2:All Du-Lite Ithacas observed have had checkered slide stops .
Note 3:Both Ithaca and Remington Rand started using serrated slide stops from when they were first approved, Colt did not start using a serrated slide stop until October of 1944.

Note 1: All Type 1 logo slide Remington Rands observed have checkered slide stops.
Note 2: 1911 slide stops with relief cut under the finger piece are not uncommon on Remington Rands with Type 1 slide logos.
Note 3: Serrated slide stops have been observed on and off Type 2 logo Remington Rands, as early as 960,000. That would put it around May 1943 time frame.