Fit OP Datejust GMT Milgauss Ref 503B

Rolex introduced the slip lock clasp. It was designed for extra security and it possesed a locking to fasten the clasp. At the beginning it was meant only for the sports models, Sea Dweller, but later for the rest of the Submariners. The materials used for these bracelets were: Stainless Steel, Stainless Steel y 9 Kt Gold, Stainless Steel y 14 Kt Gold, with gold on their laterals 9Kt Gold, 14Kt and 18Kt.
In 1954 the Flush-fit were introduced in End Pieces for all the models, which better fastened the head of the watch to the bracelet, engraving a number on the right side of each end piece.
According to the year of manufacture the number references of the end pieces were changing, the oldest (Vintage ) with 2 numbers, for example Reveted Bands with clasp ref 7836 came with an End Piece #57 . As they were modernizing the bands , they put 3 numbers e.g 257, 357 and 457 , up to have 3 numbers + letters (e.g 557B )
The end pieces were placed with a steel pin for Two Tone and Stainless Steel models . Solid gold and precious materials models use gold pins.
End Pieces sizes: 13mm for Ladies watches
17mm for Midsize watches
19mm for Mens watches 34mm
20mm for Mens Datejust 36mm or Sport watches
Jubilee and Oyster bands have different references of End Pieces.
This is for all the bands that comes with a regular clasp and not for the new style or current production models.