Hi Paul,

Thanks for the question. You will need a masonry drill bit of 16mm for the expansion bolt.

We also suggest you would start off with a smaller pilot hole with something like 4, 5, or 6mm, then go to 12mm before finally using the 16mm for the clearance hole. It does depend on the type of substrate you are drilling into, for mortar you might want to go slightly smaller depending on the quality of the mortar but for standard-facing brick 16mm should be ok. Blockwork can be tricky depending again on whether it’s a low-density aerated block, Thermalite insulation block, medium-duty aggregate block, or a heavy-duty 7N block. The best advice is, if not 100% sure, to drill a test hole in a brick or block to confirm. These expansion bolts are not suitable for work requiring sign-off by Building Control or  Local Inspectors such as balustrades/ overhanging pelmets or attaching load-bearing objects. I trust this helps.