DIY guy looking for info on drill + tap
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  1. #1
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    Default DIY guy looking for info on drill + tap

    my motorcycle has 8mm x 1.25 tapped for mirrors a rarer size, so thinkin the 10mm x 1.25 a common size would do well, so guessing material is an aluminum alloy should i drill an 11/32 hole thru then tap or can i just run the larger tap thru. thanks in advance for any input

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    Quote Originally Posted by rodhotter View Post
    my motorcycle has 8mm x 1.25 tapped for mirrors a rarer size, so thinkin the 10mm x 1.25 a common size would do well, so guessing material is an aluminum alloy should i drill an 11/32 hole thru then tap or can i just run the larger tap thru. thanks in advance for any input
    Ummm... Well technically M8 coarse standard is 8 x 1.25 and M10 coarse is 10 x 1.5. That is the standard. Drill 8.5mm to tap M10 coarse.

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    Quote Originally Posted by rodhotter View Post
    ...so guessing material is an aluminum alloy should i drill an 11/32 hole thru then tap or can i just run the larger tap thru. thanks in advance for any input
    You can't just stuff a 10mm tap in an 8mm hole. You have to drill first.

    You shouldn't do that anyway- you should helicoil it back to the original thread.

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    Some machines do use an M10 x 1.25 thread for their mirrors, and some have a right hand thread on the right side and left hand on the left side. This may be so they don't loosen in the wind? For any metric thread tapping size, subtract the pitch from the outside diameter of the thread. In your case, 10 - 1.25 = 8.75 as the tapping drill. Hope this helps. I don't have my Zeuss book to hand so not sure of the Imperial equivalent

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    I've used 11/32 for a 10X1.25 many times without issue
    8X1.25 is a very common thread size on metric motorcycles. Helicoils are your friend. If you want to go to the larger size, you might have a better selection of mirrors. Double check the mirrors you like, to make sure the threads are threads are both right hand, or not.
    Lots of this noted above, just reinforcing they are correct answers. One of my products includes a mirror mount in 10X1.25. Lots of talented people in this forum.

    Good luck!

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    Probably because 8.75 IS 11/32

    I've used 11/32 for a 10X1.25 many times without issue

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    Do you need to buy a screw? M8 and M10 are common sizes. M10x1.25 could be hard to find.

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    If you are asking if you can just "run the bigger tap in" me thinks you are not a machinist of any sort. No offense, just wanted to offer a suggestion that you practice on a scrap piece or two and make sure you can make satisfactory threads. I say this because hand drilling (meaning it will be oversize, or not straight) and tapping (break tap off in hole, start crooked, tear out top threads) may not give you the results you want if you don't have some practice with it...

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    Quote Originally Posted by rodhotter View Post
    drill an 11/32 hole thru
    Yes,if you want an M10 x 1.25 thread

    Quote Originally Posted by rodhotter View Post
    just run the larger tap thru
    God no, don't do this.



    Your best option to fix the thread is to use a Helicoil insert to get the original thread size back.

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