Good question Dicey- I’m glad you asked as it’s had me referring to all my notes and immediately uncovered what looks like a big goof on my part in the name- John & Joshua is stuck in my mind for the J & J for some reason, but my few hand written notes on these locks are all marked John & Joseph Taunton! Apologies everyone 🙁blush):
These locks are of quite heavy construction and considerably larger than most typical cabinet locks- the case and salvage is well over an eighth of an inch thick, with provision for pretty large fixing bolts in comparison. My own notes on J & J (play it safe this time) show that a few examples of locks similar to this were fitted on their safes. Some were only 4-lever detector with barrel and curtain used on lighter examples, some were heavier 6-lever detector which also featured a large brass block integrally cast into the salvage to reinforce the bolt head against sideways pressure.
My guess is that these were typically used on anything of relatively heavy construction like deed and strong boxes etc right up to and including their free standing safes, using 4, or 6 lever locks accordingly 🙁nod):
