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Thread: What size drill for M6/20 bolts?

  1. #1

    Default What size drill for M6/20 bolts?

    This is probably a really stoopid question but bought myself a shiny new Mantec snorkel at Billing yesterday (one of the new one piece plastic jobbies).

    Just looking at the fairly minimalist fitting instructions and where the bracket goes onto the windscreen surround there are two M6/20 self tappers.

    What size drill do I need for these please? Don't want to cock up drilling holes in the vehicle....
    110 Double Cab Pickup TD5 / Patriot Roof Rack / Howling Moon Roof Tent & Awning

  2. #2
    Articles Editor & Moderator Satancom's Avatar
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    Default Re: What size drill for M6/20 bolts?

    For self tappers i would guess yiou drill a slightly smaller hole? 5mm maybe?

    What I then to do is get a bit of scrap metal/wood/telephone directory and drill a hole and see how it fits
    Motors : 1980 Series III 109" V8, 2004 Mazda RX-8 (it starts sometimes too)

  3. #3

    Default Re: What size drill for M6/20 bolts?

    So an M6 bolt is a 6mm bolt is it?
    110 Double Cab Pickup TD5 / Patriot Roof Rack / Howling Moon Roof Tent & Awning

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    Links Editor & Moderator AJC's Avatar
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    Default Re: What size drill for M6/20 bolts?

    Not self tappers but an excellent bolt size article here.

    AJ

  5. #5

    Default Re: What size drill for M6/20 bolts?

    Thanks AJ. Very helpful..should have searched first

    So back to the million dollar question...What's the consensus as to which drill size I should use on the vehicle? 5mm would seem to be sensible if they're self-tappers as you want them to bite a bit as you tighten them in.
    110 Double Cab Pickup TD5 / Patriot Roof Rack / Howling Moon Roof Tent & Awning

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    Links Editor & Moderator AJC's Avatar
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    Default Re: What size drill for M6/20 bolts?

    I'd try 4mm first. That gives 1mm either side of the diameter for the screw to bite into. It too small, make the hiole bigger.

    AJ

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    Engineer callisr's Avatar
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    Default Re: What size drill for M6/20 bolts?

    5mm is the drill for an M6 tap.
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    Default Re: What size drill for M6/20 bolts?

    Quote Originally Posted by AJC View Post
    I'd try 4mm first. That gives 1mm either side of the diameter for the screw to bite into. It too small, make the hiole bigger.

    AJ
    Spot on, too small can be made bigger, too big and you are stuffed
    Self tappers have a much coarser thread then bolts so 5mm may be a little over-cooked.



    Damm.................. had to agree with AJC, i'll never hear the end of it now
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    Default Re: What size drill for M6/20 bolts?

    Quote Originally Posted by Dave-H View Post
    Damm.................. had to agree with AJC, i'll never hear the end of it now
    Cut, copied and stashed away.

    AJ

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    Articles Editor & Moderator Satancom's Avatar
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    Default Re: What size drill for M6/20 bolts?

    Quote Originally Posted by AJC View Post
    Cut, copied and stashed away.

    AJ
    Should get it made into a vinyl sticker and place it on daves truck when he's asleep at the treasure hunt
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  11. #11

    Default Re: What size drill for M6/20 bolts?

    There's no such thing as a M6 self tapping screw. Unless you mean a Tec screw in which case they have a drill incorporated into the end, so no need to predrill.

    A No6 Self tapping screw is the same as No6 Wood screw. You need a 3.5mm Drill Bit. However I would start with a 3mm as they are often of poor quality and are under size
    If it doesn't move and should; Hit It.
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    Default Re: What size drill for M6/20 bolts?

    I have a boxed set of drill bits in a metal box.

    For self tapping screws I just remove what I think is the correct drill. Then try the self tapper in that hole. Too slock and down a size. Too tight and up a drill size.

    Easy peasy..........

  13. #13
    Mechanic petefletcher's Avatar
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    Default Re: What size drill for M6/20 bolts?

    Don't force it though!
    Last thing you want is to shear the screw

    I usually use a spot of lube on the threads - just to help things along.

  14. #14

    Default Re: What size drill for M6/20 bolts?

    I should have said that they were self-tapping bolts.

    If Ada110crew is knocking around I saw you at Billing, Sunday but you were on your way out and didn't get a chance to say hello.

    A mate bought a Tomcat Challenge spec car there.

    Any ideas as to good pay and play sites in East Sussex/Kent to have a play in it?
    110 Double Cab Pickup TD5 / Patriot Roof Rack / Howling Moon Roof Tent & Awning

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