TheSamba.com :: View topic - Tapping out an M11 to M12? Seat belt bolt question.

Wed Aug 07, 2013 3:48 pm

Failed attempt at replacing rear bench seat. The z-bed in non campers is held to nuts welded to the body which are M11 x 1.25, the same pitch and thread as the seat belt bolts. I knew going into the project that these bolts love to cross thread, and was careful but somehow crossthreaded one severely, and two just a little.

I'm not even sure an M11 x 1.25 tap could save the day, but they are certainly not available locally and reasonable cost shipping on Amazon is at least two weeks.

I have an M12 x 1.25 tap but have never used a tap for anything other than thread cleaning. Is upsizing these bolts to M12 using the tap I have a bad idea? These nuts are welded to the body so I don't want to screw it up. Thanks for any input I'm not exactly sure how obscure a question this might be.

-Rob

Wed Aug 07, 2013 3:56 pm

Strange as it sounds, I think you may find that those are really 7/16" bolts. Take a good one down to a decent hardware store and match one up. Then buy a 7/16" tap of the correct pitch.

Mark

Robw_z wrote: Failed attempt at replacing rear bench seat. The z-bed in non campers is held to nuts welded to the body which are M11 x 1.25, the same pitch and thread as the seat belt bolts. I knew going into the project that these bolts love to cross thread, and was careful but somehow crossthreaded one severely, and two just a little.

I'm not even sure an M11 x 1.25 tap could save the day, but they are certainly not available locally and reasonable cost shipping on Amazon is at least two weeks.

I have an M12 x 1.25 tap but have never used a tap for anything other than thread cleaning. Is upsizing these bolts to M12 using the tap I have a bad idea? These nuts are welded to the body so I don't want to screw it up. Thanks for any input I'm not exactly sure how obscure a question this might be.

-Rob

Wed Aug 07, 2013 3:58 pm

If tapping it doesn't work out. Investigate using a blind nut... aka rivet nut... I used them all over my van to create threaded holes for mounting interior panels and cabinets. Search for them on amazon or where ever.

http://monsterfastener.com/itemview.aspx?itm=BNIS-053&gclid=CJux3ui27LgCFYtDMgod31UA9w

Wed Aug 07, 2013 4:01 pm

tap it out carefully, once you have it started, i always turn turn in 1/4 turn, then back off 1/2 a turn, use cutting grease or some kind of lubricant, and don't hurry.
turning back after each cut will clean the tap, and shold leave you with a decent thread when you are done.
i have watched people just wind the tap through the hole and end up with a mess.
take your time, be sure you start off square, and take your time.

Wed Aug 07, 2013 4:08 pm

crazyvwvanman wrote: Strange as it sounds, I think you may find that those are really 7/16" bolts. Take a good one down to a decent hardware store and match one up. Then buy a 7/16" tap of the correct pitch.

Mark

They are actually metric 11 x 1.25 threads
Darn close to 7/16 x 20 used by the USA
So close that they will thread into each other.
11mm 0.4331
7/16. 0.4375

Dave

Wed Aug 07, 2013 4:12 pm

They are so close that the factory VW Parts data says they are 7/16" bolts.

Mark

djkeev wrote: crazyvwvanman wrote: Strange as it sounds, I think you may find that those are really 7/16" bolts. Take a good one down to a decent hardware store and match one up. Then buy a 7/16" tap of the correct pitch.

Mark

They are actually metric 11 x 1.25 threads
Darn close to 7/16 fine used by the USA
So close that they will thread into each other.

Dave

Wed Aug 07, 2013 4:16 pm

If you end up needing to tap them to M12x1.25 (which should work just fine), make sure you run a 27/64" drill bit (actually, the proper drill bit diameter for tapping a M12x1.25 is 10.80mm, but a 27/64" drill bit is 10.72mm which will work fine) through them before attempting to tap them. Otherwise you could end up breaking off the tap inside the nut and then you would have a real mess to deal with.

Wed Aug 07, 2013 4:20 pm

And..... Once you resize that hole purchase a proper grade hard bolt!

Not just any bolt can be used in such a critical safety point! A lesser bolt will simply shear off when stressed upon impact leaving your passenger free to flail helplessly about inside the vehicle at impact.

Dave

Wed Aug 07, 2013 4:29 pm

all seat belt anchors made on Planet Earth are spec'd to be SAE bolt threads

dunno re the seats themselves

Wed Aug 07, 2013 4:31 pm

Here, VW says they are 7/16" used on many years and many models. The first is a shorter one, next a longer. Both described as 7/16" bolts, used on vanagon bench seats and seat belts.

http://www.jimellisvwparts.com/products/Volkswagen...57799.html

http://www.jimellisvwparts.com/products/Screw--hex-hd/5341012/N98951601.html

Mark

Thu Aug 08, 2013 1:24 am

Thanks for all the suggestions and input!

From what I've read I am tempted to try a 7/16 x 20 tap, which is available locally, and try and re-use the factory bolts. If not plan B is M12. Thanks to Chris for the tip to drill and the size!

I also saw a trick on some muscle car forum to thread the tap through a nut first(in this case a 7/16 nut) and washer, and hold them against the surface to help with starting it straight, which is the part I'm most worried about.

This whole thing happened because I thought since I could pull a Z-bed from a junkyard van solo, easily, I could also install it solo... Not so! Not the whole assembly at least. You can only hold up one side at a time, and that angle tends to force the bolts to cross thread. If installing alone, unbolt the cushioned sections first!

-Rob

Thu Aug 08, 2013 1:32 pm

crazyvwvanman wrote: They are so close that the factory VW Parts data says they are 7/16" bolts.

Mark

djkeev wrote: crazyvwvanman wrote: Strange as it sounds, I think you may find that those are really 7/16" bolts. Take a good one down to a decent hardware store and match one up. Then buy a 7/16" tap of the correct pitch.

Mark

They are actually metric 11 x 1.25 threads
Darn close to 7/16 fine used by the USA
So close that they will thread into each other.

Dave :lol:

Sun Aug 11, 2013 2:27 pm

For thread posterity I will confirm that a 7/16 x 20 tap works very well in place of an M11 x 1.25, which is hard to find.

I would call the difference between the two "negligible but existent" meaning you can tell there is a bit of a difference, as evinced by a more than usual amount of metal carved out by the tap, but nothing to worry about.

-Rob

Sun Aug 11, 2013 2:30 pm

Yep, the similarity was mentioned.

Glad that you got it sorted out!

Dave

Sun Aug 11, 2013 2:55 pm

They are definitely 7/16 bolts, all of the seat belt bolts in the van are that size just like crazyvwvanman said.