What size mason drill bit/Tapcon screw to fix sunken box's ?

[Monkeh]

mark box fixing holes, 6mm drill, red wall plugs.

Tapcon screws are the devil's children.

OOI what's wrong with tapcon screws? Seen them but never used em!

They're a bit hit and miss. You have to use just the right size drill for the material, and half the time you have no idea what that'll be until you try and use them.

Plugs are just easier for most things.

 

[securespark]

I had a sparky mate who was pulled up on his NICEIC assessment for using countersunk screws to secure backboxes. He was TOLD there was a chance of sharp edge on the screw snagging the insulation on the conductor.

He was told that only roundhead screws were acceptable

That's how I was taught as an apprentice!

Black japps.

 

[333rocky333]

You can blast a 5.5 drill right through the hole in the box then tap a red plug through and do up.

Oh - I thought I was probably the only person who did that - so I didn't dare mention it here

Kind Regards, John

Me too sds or impact drills blast through the thin metal easily if needbe.
Seriosly though, going through the existing slots a 5.5 barely has to cut any metal out

 

[JohnW2]

You can blast a 5.5 drill right through the hole in the box then tap a red plug through and do up.

Oh - I thought I was probably the only person who did that - so I didn't dare mention it here

Me too sds or impact drills blast through the thin metal easily if needbe. Seriosly though, going through the existing slots a 5.5 barely has to cut any metal out

Indeed. In fact, as sparkwright said, a 5.5mm drill will acually go through the hole of many (but certainly not all) back boxes withgout having to cut metal at all. However, as you say, if it does have to cut a small amount of metal, it does so easily!

Kind Regards, John