Holley bowl screw thread size
 

I am rebuilding a pair of old Holley Dominator carbs.

One has had several Helicoils added for the bowl screws and one thread is about stripped out and needs a helicoil. I know Holley sells a kit for this with tap, install tool and inserts, #26-2.

I would like to know what the original thread is so I can get a tap and die for that size. I am thinking it is 12-24 thread but haven't found if that is true anywhere. A couple of the helicoils wont let the screw start so I thought I might be able to run a tap thru them and also dress up the screw threads themselves. I might find the Helicoil kit cheaper in the Mcmsaster Carr catalog too if I knew the size.

Yes 12-24.Also quick fuel sells bowl screws that are a little longer.Bill.

I agree with 12X24 threads, but i don't think you will be able to run a tap into the helicoil that's already installed since most helicoils are stainless.

JMO

Zip.

Holley
 

Well there is an issue with the helcoils already installed. I realize the stainless is harder than just a regular thread, but thought I could get a tap to chase a present thread. No luck there. I can't see anything wrong with any of the helicoils, they don't look bad. The carbs were together and running when the engine came here for rebuild. It was just an after thought to go thru the carbs. The original screws came out fine, but won't start again. I have had to pull out helicoils in the past, but never on this small of thread. I have chased the threads on the screws with a adjustable die and they go right in the good carb threaded holes.
If I can get the old helicoils out without damaging the threads in the carb body, I now have new helicoils to put back in.