threading aluminum

I want to tap the adapter plate on my fuel cell so i can bolt my clamp plate down to hold my fuel pump in. I looking to use a 1/4" ss allen cap bolt but i dont know if it would be better to thread it for 1/4-28 or 1/4-20. I dont know if one will hold better then the other. BTW there being threaded into a 1/4" adapter plate.

Edited: 10/28/2005 9:35:10 AM by bagged85

a 28 thread will hold better plus loctite them fuckers, just make sure u you put anti seize on the tap b4 u do each hole.

actually a 1/4-20 will hold alot stronger then a 28 as long as it it going into a 1/4" thick plate.

you didn't menton the thickness of the plate you are tapping.

i would go with the 28 more treads per inch. make sure when you tread the bolts in you don't over tighten them because if you do you will rip out the treads.

Originally posted by pootytang



you didn't menton the thickness of the plate you are tapping.

yea i said 1/4 adapter plate

Originally posted by bdydrp18



i would go with the 28 more treads per inch. make sure when you tread the bolts in you don't over tighten them because if you do you will rip out the treads.

thats why i was considering using a 20tpi versus a 28 because i thought the finer thread will strip out easier.

im also using a ss fastner....that should be good for a gas tank right, i dont want it to rust and contaminate my fuel system.

Always use a coarse thread when tapping a weaker material than the fastener and make sure that you get at least 4 full threads. The stress on a fastener is greatest at the first 4 threads. The reason for the coarse thread is fine threads have more mechanical advantage, on soft metals this helps to "pull" the threads out since higher torque values are easier to obtain. That is the reason they are used on cylinder heads, suspension components ect. Ever noticed studs with fine threads on one side and coarse on the other?

Oh yeah, you said 1/4" thick so 20 tpi is 5 threads for 1/4" so it's fine.

^ thanks andy, thats what i had figured because its actually 1/4 plate over 1/8" sheetmetal on the fuel cell itself so it willbe 5/8 overall. I just wanted confirmation of what i had originally presumed. thanks everyone.

hell yeah, on 1/4" use the course threads