Retapping M8-1.0 to M8-1.25, any harm?
 

Dang it. I grabbed the wrong tap, M8-1.0 instead of M8-1.25, for a hole in the seatback. Are there any harm in retapping the same hole to M8-1.25? Will there be enough meat for M8-1.25 bolt to bite on? This is not a high stress area. Thanks in advance.

How deep is the hole ... 1/4 or so? I would imagine that you should be alright retapping. If you had done the coarse thread first then wanted the fine I would think that it might now work as well. Being the finer thread was first I would imagine the coarse 1.25 would still catch enough meat. I think you'll be ok.

Do you not have a M8 1.0 bolt to use or just want to keep it all M8 1.25 for consistency purposes?

Thanks Leiden.

I'll see if I can find M8 1.0 bolts at Home Depot today. if not, I've seen plenty of M8 1.25 there and just retap the hole. Andy

Try fasenal. They have pretty much everything. Should also have Allen head in diff grades. A bag of 25 should be about 10-15 bucks. Lowes and HD never have the weird fancy stuff, lol.

Hey Andy. I wanted to check so I swung by my shop. I have a bag of m6 1.0 by 20mm stainless socket(Allen head) screws. How many do you want. I bought a few bags to change out the steel fender fasteners. Let me know.

I wouldn't do it Andy. Find a -1 bolt to fit or weld it, redrill, and retap. The major diameter of the two are the same. The finer pitch bolt, having smaller threads, has a larger minor diameter by necessity. The corresponding tap drill is different (larger) if you check. So there will be very little thread engagement if your try to tap coarser.

Loctite/permatex has a cheap & easy thread repair kit for light duty apps.

Helicoil it otherwise.

The minor dia may be different but depending on what size drill was used that could vary. The difference is 0.2mm. The major for both is the same IIRC. At this point if a M8 1.0 bolt isnt used you really have nothing to lose by re tapping. In the end if it doesnt work you will have to weld and retap anyways. I have seen alot of guys fudge it and it works most of the time. Not like it a exhaust manifold stud or another high stress area. The best way as Stephen mentioned too is to get the right bolt and call it a day.

Andy did you ever find a 1.0 bolt?

Thanks for all your inputs. I think all options are worth considering. I needed a M8 flathead Phillip screw and local HDs only carry up to M6 size. I'll try Lowes to see if I can find M8-1.0 and use as is, or take a chance and retap to M8-1.25. Last resort would be locktite thread repair or weld and retap. Andy

Andy. I just realized I said I had m6 not m8 ... no help at all with that post, sorry. I did find this on Fastenal website. I can usually find just about anything there. I found M8-1.0 flat socket screws. No Phillips from what I saw.

http://img3.fastenal.com/productimages/39940_hr4c.jpg

Here is the search page with all the lengths.

http://www.fastenal.com/web/products...%20Screws%22|~