# Drilling size for self tapping screw



## sallytrafic (Jan 17, 2006)

Hi

I need to screw some self tapping screws into the outside skin of my van.

They are #8 and the outside diam is 4mm. As near as I can judge the centre of the screw is 3 to 3.2mm diam. What size drill do I use to minimise distortion of the surface whilst making the STS do its job?


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## maddie (Jan 4, 2006)

Hi Frank you should use the centre of the screw -not the threaded bit ie in your case 3 mm or poss a v/little smaller if drilling into ali
terry


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## 101411 (Oct 15, 2006)

Hi Frank

Yupp a 3mm drill is the baby you need


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## sallytrafic (Jan 17, 2006)

Thanks Dazzer & Maddie


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## sergeant (Jun 7, 2006)

Hi all, If you are screwing into the outside wall of the van then for maximum strength you do NOT drill a pilot hole. The idea of a self tapping screw is it cuts & FORMS its own thread & is 3 times stronger than when a pilot hole is drilled, Steve


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## Spacerunner (Mar 18, 2006)

sergeant said:


> Hi all, If you are screwing into the outside wall of the van then for maximum strength you do NOT drill a pilot hole. The idea of a self tapping screw is it cuts & FORMS its own thread & is 3 times stronger than when a pilot hole is drilled, Steve


Does this also apply to GRP 'vans.?


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## sallytrafic (Jan 17, 2006)

sergeant said:


> Hi all, If you are screwing into the outside wall of the van then for maximum strength you do NOT drill a pilot hole. The idea of a self tapping screw is it cuts & FORMS its own thread & is 3 times stronger than when a pilot hole is drilled, Steve


Somewhere in my mind I was thinking the same thing but wondered if a 1mm hole might be good to get it started. I was going to punch the spots anyway for accuracy


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## sergeant (Jun 7, 2006)

Hi Spacerunner. For GRP you do need to drill a pilot hole slightly larger than the shank or the GRP will simply break up. For a no 8 or its equivalent 4mm you need a 3.2 mm or in good old english a 1/8 drill, Steve


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## Spacerunner (Mar 18, 2006)

Thanks Steve, am still trying to work up the courage to attach an awning skirt rail to a 6 week old 'van. Is there such a thing as a self-adhesive skirt rail? :roll:


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## sergeant (Jun 7, 2006)

Hi Spacerunner, Unfortunately not strong enough that way or I would be doing them like that at work to save time, Steve


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## gromett (May 9, 2005)

"self" is the key word. I had an argument with a guy the other week about this.

Ended up with leaks in my roof after he had finished. Wished I had kept my mouth shut or done it myself after he left.

Self tappers will make their own hole and self tap if used correctly. Minimal (if any) sealant is needed after.

Put your elbow into it pressure wise, and it will drill and tap on its own. Best type of fixing IMO.

Karl


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## baldlygo (Sep 19, 2006)

gromett said:


> "self" is the key word.


Not sure I would agree with that :roll:

My understanding is that when they first became widespread (1960's/70's?) it was the "tapping" which was the key word - which meant that you always needed the pilot hole first. It is only in more recent times (1990's?) with the widespread use of electric drill screw drivers that fully self tapping screws became available and are now the norm.

Please bare in mind that "My understanding" are the key words in this post :wink:

Paul


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## Scotjimland (May 23, 2005)

Self tapping screws can indeed be used without a pilot hole in ally but not in mild steel.. I prefer to drill a pilot hole. 
By design they are Self Tapping.. not Self drilling.

But there is also a self drilling/self tapping screw, not to be confused with the former, much better than forcing a self tapper which can result in distortion of the ally.

Note the drilling tip of the screw >










~Self Drilling Screws~

Pop rivets are often a better choice, stronger than any screw.. I use them where ever possible in preference to screws.


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## eddievanbitz (May 1, 2005)

I agree with Scotland Jim and like self drilling screws. We use loads of then so can chuck a handfull in a bag if you still haven't done the job Frank. Usual address?


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## maddie (Jan 4, 2006)

Hi been reading replys with interest--Frank asked --- to minimise distortion----hence advise to drill pilot hole---look at ScotJimland pic and it clearly shows a drill bit on the tip of the screw which is the size of the shank.I use these screws all of the time and have done so for the last 10 years or more since I first came across them.I think the distorstion bit ocurs when trying to force the shank through the metal-the screw bit pulls it in aiding grip but if the right size thread is used(curly bit)it grips onto the face of the metal.
terry


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## sallytrafic (Jan 17, 2006)

Who'd have thought a simple question could lead to all this. Keep it coming I'm sure this thread will answer lots of questions in the future.

(Thanks for the offer eddie but I aleady have S/S pan head self tappers which for this application I prefer to counter sunk.)


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## maddie (Jan 4, 2006)

Hi try self tapping into chipboard or MDF with anything but the thinnest gauge screws & you will see what happens 8) :wink: ---We also use thin very sharp Drywall screws--
terry


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## DubPaul (May 10, 2005)

great timing in the thread as I need use self tapping screws on the inner wing of my classic car and was scared to do anything! I will drill a small pilot hole.


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## maddie (Jan 4, 2006)

Hi just another note on the drywall type screws(thin self tappers) if drilling into thicker steel or mdf without a pilot hole they get halfway in then snap!
This causes real probs if it is on show.
terry


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## cabby (May 14, 2005)

I see no one has mentioned to put masking tape or similar to protect the surrounding area when drilling.better safe than sorry.If you use pop rivets you still have to drill hole.double sided tape will work but you still have a mess where it sticks and it will lose its strength.

cabby


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## thehutchies (Jun 25, 2005)

I agree with the suggestion for using drywall screws.
I recently converted a panel van to be used as a mobile clinic, similar construction to a motorhome, and the drywall screws were excellent.
I never drilled pilot holes but they would go through anything.
They are very thin, though, so need care with the torque setting on the driver.


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