Natty Takeup wrote:
I wonder if anyone can help. I need to fix 15 x 2 metre long metal rails
("T" section) vertically to a concrete wall. I'll be using those 'self
tapping' bolts that require a 6mm hammerdrill bit. I will need to drill
8 holes in each rail.

Q.1. How much larger will the rail holes need to be 6.5, 7.00, 7.5mm Etc?

Sounds like seven should be ample - do the fixings not specify a
clearance hole?

Q.2. Nowadays, which drill bit manufacturer is considered high quality?

What sort of drill? For a SDS bit then most makes will be fine as long
as you avoid the 3 for a quid range from a pound shop.

For conventional masonry drills, then the Bosch multimaterial bits are
very good.

Q.3. Is there a good, reliable on-line source to the above? Many thanks.

Take your pick: Screwfix, Toolstation, Axminster etc.

--
Cheers,

John.

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