The only problem that I have encountered with the Avery drill stops was that the grub screws would wear if I over tightened with the Allen key, eventually rendering the grub screw/drill stop useless.
There were no spares listed in the Avery catalogue so I contacted Diana at Gloster Air Parts and she now sells part number #1100-R, which contains 4 grub screws and an Allen key for £1
