NMot knowing any better, I assume the "1" inside the original crutch tip means it was 1-inch diameter.
Here is a knife on eBay that looks as if the rubber crutch tip was smaller--notice the bulge where the handle ends inside it.
https://www.ebay.com/itm/Randall-Made-Knives-Model-18-7-5-Solingen-Crutch-Tip-Riveted-Sheath-Vietnam-Era/132797943083?hash=item1eeb5fcd2b:g:fI4AAOSwtM1brQiY
Perhaps it was replaced by an owner at some point?
The Model 18 at the above link looks to be an older knife, and it might be expected that an original rubber tip would have degraded over the years.
Or possibly the shop used different ones at different times?
Larry
_________________________
Larry W. Williams
RKCC #CM-041
ABKA #046
RKS #1246