I saw this one being sold on eBay last year (or maybe another one that someone had made). This is not the original factory set up for the MAC bayonet, this one has been home made using one of the atchisson 4 blade throwing knives. At some point in the mid 80s, SWD decided to discontinue sales of the atchisson throwing knife and converted them into bayonets. The genuine factory bayonet had a threaded lug that screwed onto the barrel threads. Not a clamp like this one… it also had the patent number milled off the blade and was marked with the SWD rollmark, not RPB. This is an earlier example of the RPB atchisson thrower that someone made bayonets out of with some kind of clamp mount, it is an aftermarket home workshop job and not the genuine Cobray bayonet.