Wow – that does seem an excessively hefty price, even assuming that they think surveyors are wealthy people for being able to purchase all that surveying gear.
I’ve built a couple of adapters for 3/8 to ¼ inch by cutting a couple of 3 inch diameter wooden discs from 12mm plywood and 9 mm plywood.
I then drill a hole in the 12mm disc and fit a 3/8 inch threaded insert from Bunnings. These are the ones that table legs with a male 3/8 bolts screw into. You hammer these into the slightly under size hole and the 4 bent over tabs bite into the wood to prevent the socket from rotating.
I then fit a ¼ inch bolt sunk into the 9mm wooden disc and then screw and glue the 2 discs together which gives me a 3/8 female socket underneath to a ¼ male bolt protruding from the top.
I suppose you could do something similar but use a 5/8 nut inset into the 12mm disc and held in place by drilling into the side of the disc, part way into the nut and inserting a couple of thin round nails to prevent the nut from turning?
