It appears to me that the No. 15 and 19 padlocks were introduced around the end of the 1960s or beginning of the 1970s, and that they have always had bumpers, originally, however, of a different shape from the later blue bumpers. See this recent eBay auction for a gold (?)-plated early No. 15 with said early bumper that appears to have been issued in 1971 for Master Lock’s 50th anniversary. Early No. 19 padlocks have a red-colored bumper of this shape, although there is also one currently on eBay with a “chocolate” bumper. I have never seen a No. 15 or 19 that was not made with a bumper. There is a patent for a bumper from the late 1960s, patent no. 3453758, that may be for this bumper. In the design in the patent, one of the laminated plates is of a smaller size, and the bumper has a lip that fits into the resulting gap, holding it to the padlock body. In the later blue bumpers on later padlocks, several laminated plates, matching the height of the bumper, are of a smaller size.
It is apparent that the No. 5 and the smaller models got their bumpers at a later date; I do not recall ever seeing a No. 5 or smaller padlock with the above early bumper. I’m surprised that they only started being made with bumpers as late as 1987; I had previously thought that they got their bumpers sometime earlier than that.
Note that there was also a solid-metal bumper design patented that would apparently be used in place of some of the laminated plates. Patent no. 3835676 from the 1970s is for this design. It appears that it may have been used on the original No. 37 “Armorlock” shrouded-shackle variant of the No. 3 and the wide No. 101 padlock.
The above, of course, is relevant to the laminated pin-tumbler padlocks. It appears to me that the laminated warded padlocks got their bumpers around the end of the 1990s, around the time that Master Lock outsourced manufacturing of them to China.
