RCS Heavy Boer-War Plug-8 Handcuffs
This cuff was manufactured by the RCS company in England during the Boer War (1899-1902.)
The lock on these most uncomfortable and restrictive handcuffs is based on a captive bolt and a plug. The bolt locks the cuff and the plug provides for security by limiting access to the bolt and as a means of preventing dirt and such from getting into the mechanism.
To unlock the cuffs, first use the two pronged end of the key which fits into the plug and unscrew it from the lockcase. The plug is a short threaded cylinder with two small holes in its head where the two prongs on the key fit. Next the other end of the key is screwed into the lock until it has passed the lockcase's threaded portion completely. The threaded part of the key is 5/8" or so in length. It ends with a cutout that is + shaped which inserts into the nut in the lockcase and allows it to be turned and thus push the bolt, which is screwed into it and is welded to the other end of the cuff, out.
To lock the cuff, the key is screwed in, the + is inserted into the nut and turned to pull the bolt in, the key is then screwed out and the plug is screwed in with the pronged side of the key.