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I've heard that if using an SDS drill I should go a size down for drilling for rawlplugs.

I want to use red rawlplugs which source vary on saying I either need a 5.5 or 6mm hole for. I am based in the UK if there if is any difference in the colours.

What size SDS bit should I use to drill a suitable hole.

Thanks

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    Did you check the packaging that the plugs came in? Manufacturers usually list the hole size in the product instructions, – Michael Karas Oct 27 '19 at 14:46
  • What is the material you are drilling into? – GdD Oct 27 '19 at 16:12
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5.5 or 6mm sounds about right for a red plug, however not all reds are created equal, drill bits also vary and the material you are drilling into makes a difference as well.

If I'm drilling into a softer material like plaster (especially old plaster) I will always start with a slightly smaller bit than called for in the instructions, even 1mm less, this is because softer materials can sometimes allow the bit to drift and you end up with a larger hole than the bit. Even with harder materials like brick I will also go slightly smaller, .5mm less, than called for just in case my bit takes out more material than expected. I drill, then I try to hammer the plug in, then I will step up a size if needs be. I'd rather have a really snug fit and trim a bit of the plug off at the wall then have one that goes in but is slightly loose.

With SDS bits I would use the same approach, how much depends on the bits and how aggressive the hammer drill is (presuming you are using one). If it's brick or concrete you can start off with a 5mm and work your way up.

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  • Bosch Drill with Bosch bit and RawlPlug brand plugs - drilling into stone. In the end I tried the 5.5 and the plug didn't go in too easier so I went to the 6 and that was better. Thanks for your help. – 111111 Oct 27 '19 at 22:26
  • Glad it worked for you @111111 – GdD Oct 27 '19 at 23:10
  • Honestly, this is pretty bad advice. 1. plugs should never, ever be used for softer materials. They're strictly for masonry 2. Drilling too small is pointless and likely to cause trouble - the correct size will give best results. Smashing them in risks breaking them (a complete PITA to get out), if it goes in then your screw sizing will be off. 3. plugs need to go all the way in, if you lose more strength from this than you might gain from snugness. 4. 6mm SDS doesn't need a pilot hole - this risks the drill jumping through the hole or bucking on a hard bit, giving you a worse hole. – Niall Oct 29 '19 at 13:08
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Both 5.5 and 6mm plugs are available and both are red.
Rawlplug brand are typically 6mm.

Annoyingly while 6mm bits are very common and 5.5mm bits are pretty rare, 5.5mm plugs are more readily available.

Does this make a difference?
Only a little, you should follow the instructions for best results but there should be enough wiggle room to make it work. A 5.5mm plug in a 6mm hole will work unless you're right at the limits (which you shouldn't be anyway) - especially if using 4.5mm instead of 4mm screws. Ideally plugs should be tight in the hole and it's normal for them to need a gentle tap to get them in, but if you have to swing the hammer there's something wrong.
If they're too loose then they'll spin in the hole when you try to screw into it.

Note on use:
The talk of materials above caught my attention. It seems to be a thing in some places to use plugs for plasterboard - the should strictly only ever be used for masonry (which I assume you are if using a SDS drill).

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