OK
I made some and it was a piece of piss
Member on here called creaser was selling machined-out pro2 QR adaptors as 15mm. Turned out that they worked fine for that purpose because they are the same as the 15mm ones regarding internal diameter, just with some extra 9mm guff on the ends. He was selling the machined ones cheaply and, since I knew I was going to further butcher at least one end, I thought I’d take a chance on them. They were really nicely machined FWIW. I did wonder if people would be interested in getting him to machine these bulb sets poshly but fiured not many folk still used bulbs
I’d had a look at a set of the QR ones against a bulb before and already wondered if I could bulbify them easy enough. In fact all you need to do (for a 6 bolt bulb – I learnt today that 5 bolt are different) is chop off a bit of one of the end pieces, just at the point where the (easily removable) silvery metal ring sits. I used a hacksaw – it’s very soft alloy – and then tarted it up a little with a file.
SO, get some 15mm caps and chop one up. I’m as close to certain as I can be that the “real” 15mm ones will work the same, though mine were machined-down QR ones as I said up there