I dare say that some might have been fitted for the initial trials on the original trials rifles but I can tell you with certainty that there was never a piling swivel ever issued or available for the production No4. By the start of series production, the notion of piled arms was a thing of the past. From the earliest non illustrated 1941 dated flimsy parts list to the last, a piling swivel wasn't an option - unless anyone knows differently.