The Panhead & Flathead Site

Author: MikeColaizziPghPA

Hello,

Since many of us have bolted on various parts and lost original bolts in reassembling our bikes, I was wondering: when do we use fine and when do we use coarse threaded bolts? Possibly a machinist or engineer here could answer. Thanks in advance for any help.

Post by fourthgear

Hi
I'm not a machinest , but I use fine threaded where ever possible ( which is whats on our old scoots ) they have better holding power because of more threads per inch. I use thread locker on all faseners including nylocs!
Just my opinoin and we know how that goes. good luck.

Post by Mbskeam

hello,
lock tight, a pans best friend, did this to all most all the hard ware many years ago. and they have held up fine. on the ones I did not do the first time. they have since been done . and nylocks work great also.
As for the threads. I think that fine in steel is good, but in alum. course will have more thread strength, due to the pitch being farther apart, ie... more meat in between pitches of thread. exsample use 10-24 for alum 10-32 for steel
mbskeam

go to the hard ware store and ask for 1/4-24 and see what you get for a answer

Post by billy

Yes Harleys & Loc-Tite go well together. & done properly stay together.
Done properly= no oil/grime on threads. Wink

Post by Sidecar

There are too many variables !!!!
Soft mat'l coarse threads ?
Hard material fine threads ??
Little stuff too small for coarse threads ??
Big stuff needs coarse threads for more holding power ?
I have had problems with fine threads on large nut/bolts in jerking/pulling/shaking applications. Seems that the threads get boogered up and you can't get the nut off and on again.
Loc-tite way too expensive. Clear nail polish much cheaper. Been using it for 30 years without any problems. I have converted a lot of others also.

Post by BigMike

Another thing to consider, torque on coarse and fine fasteners acts differently. A coarse bolt overtorqued will usually break (many coarse fasteners are grade 2). A fine thread fastener overtorqued will strip the threads. (usually higher tensile strength, grade 5 or above makes the thread surfaces the weak point) FWIW, when in doubt, I use fine thread, torqued carefully with the proper lockwashers, and lock-tite or I use nyloc nuts. Vibrations seem to have more effect on coarse threads.