Petcock Screws - Correct Tap size?

staggerwing · Post by **staggerwing** » Sat Jun 30, 2018 6:06 pm

Good evening from Marietta, Ohio. Last night I was installing the popular aftermarket petcock on the bottom of my CA78 gas tank. One of the screws was going in kind of tight so I was screwing it in and out until I got close to having it fully inserted. It got tight and I ended up snapping the head off!
This morning I drilled the screw out of the nut and some of the threads were effected. I'd like to run the proper tap through the nut to try and salvage the threads and was wondering what tap I should use. Also, if that doesn't work, has anyone had to drill and tap the nut slightly bigger and if so, what size did you end up with? Any other ideas? Thanks.

staggerwing · Post by **staggerwing** » Sun Jul 01, 2018 11:15 am

It appears to be a 4MM bolt. My thoughts were to chase the nut with a M4 tap and if I can't get enough bite after that I would drill and tap for a 5 MM bolt.

G-Man · Post by **G-Man** » Sun Dec 30, 2018 4:36 am

Those are JIS screws. Did you get it fixed?

G

staggerwing wrote:It appears to be a 4MM bolt. My thoughts were to chase the nut with a M4 tap and if I can't get enough bite after that I would drill and tap for a 5 MM bolt.

staggerwing · Post by **staggerwing** » Sun Dec 30, 2018 8:52 pm

Yes. I had to drill and tap it for an M6 bolt.

G-Man · Post by **G-Man** » Mon Dec 31, 2018 2:30 am

Good job!

G

staggerwing wrote:Yes. I had to drill and tap it for an M6 bolt.