Just been looking through the screw fix book for screws and why oh why are some metric ( dia mm x length mm ) and some are imperial ( gauge x length inches ) and not forgetting ( M dia x length mm ) so my question is when you buy a drill it's in mm dia how do you know what screws will be suitable???
Rich
Doesn't matter. For small screws in softwood you can often get away without a pilot hole; when you do need one, the size of the pilot hole is not critical. p6 of the Screwfix cat has a handy-dandy little table illustrating the point - if you want to be bothered, calculate the difference between the actual sizes of the metric vs imperial pilot holes and you'll see some variation.
Bottom line - buy whichever set of sizes you feel comfy with and which has the flavour of screw you're after.
Stefek
I aggree and the gold screws SF sell are very good with power drivers. Try one of their selection packs and you won't want to use anything else.
Until you've tried torx drive screws with serrated ends, such as Spax. Then you won't want to use anything else. ;-) I don't care what they cost; if they doubled in price I'd still buy them.
OOOOp's sorry forgot to say that I was on about masonry drills with wall plugs and screws!!!! Rich
In which case the screw size is less critical than the plug size. Brown plugs > 7mm holes, red > 5.5mm, yellow > 4mm. Screw to fit plug.
The SF gold scres have serrated ends. I was attracted by the look of those Spax but note SF seem to have stopped selling them...
Not the ones I bought from screwfix - but this is minor compared to the torx heads.
I used to buy them from screwfix, but since they stopped I buy them from axminster. The big difference is in how much torque you can apply to the head. With all pozi heads there is some tendency for the bit to cam out. This is totally absent with torx heads.
I'd never go back to pozi, and find myself hating it on the odd occasion when I have to use it.
It's something you find out with trial and error! But as a rough guide: yellow plug > 4mm head screw, red plug > 6mm head screw, brown plug > 8mm head screw.
M designations are only used for parallel thread screws/bolts, so are irrelevant to this discussion. But for info, and M6 is
6mm diameter, and M8 8mm etc.
Ah but if you look in SF for coach screws you will see they are M sized for dia with a metric length so this is what I was getting at. So if I was to drill a 7mm dia hole in a concrete block wall and put a brown wall plug in it what is the bigest dia bolt I could fit in it using coach screws, the ones I have got from B+Q have a 6mm dia accros the shank so these are M6 then, what do you think??
Rich
Ok, that's true.
No, 6mm shank is way too big for brown plugs. For that size, you will need the next size up plugs (sometimes blue, sometimes grey), which require a 10mm hole in the wall. Make sense?
Hmmmmmm ok but this is what I was originally on about how do you work it all out or is it just trial and error?
Rich
Partly trial and error, partly logic. Say you want to use a screw with a 6mm dia shank. And say the plastic plug will have a wall thichness of 2mm (reasonable assumption). That means shank
It's experience you quickly acquire. Ten minutes' browsing in your local d-i-y shed should do it: most wallplug packaging - and the center strip which holds some brands together, e.g. Plasplugs - will tell you what size of screws each wallplug is intended for, and what size hole (and thus drillbit) you want. Experience will also tell you how to achieve the actual hole diameter you want in particular materials - e.g. in normal "hardish" house brick holes will come out more or less as advertised; in softer materials holes tend to get bigger by a little bit. You'll also learn to compensate for that in other ways - e.g. if you find the plug is turning in a hole which turned out a bit too big, pull the plug out using the screw, drive the screw into the plug a little way further
- which makes the plugs a tad wider - then press the now-wider plug into the now-snugger hole.
Honestly, it's not *that* critical: the tendency at first is to believe a very tight fitting is stronger, whereas an overtight one in fact tends to chew up the plug rather than have it expand nicely in multiple directions.
Hang in there... cheers, Stefek
Right ok will look at the plug packaging and go with that and experiment!!!!!!
Thanks
Rich
I buy plasplugs by the hundred, and screws by the boxful. When it comes to the time when I need to screw something to the wall it is instantly obvious which size plug I need.
Trying to order screws and plugs in a specific quantity to do a specific job sounds like a rather costly and time wasting exercise!
PoP
There's a conversion table in the Screwfix cat
-- Die Gotterspammerung - Junkmail of the Gods
Until you put a bunch of them in with a power driver and no pilot holes, holding them in your fingertips to start them.
Then you look down at the state your fingers are in !
-- Die Gotterspammerung - Junkmail of the Gods
IMHO, >7mm holes are grey, because I always use nylon plugs on big holes. It really only makes a difference in brick or concrete, but the nylon ones are stronger.
-- Die Gotterspammerung - Junkmail of the Gods
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