Trailer hardware - course vs. fine

BoatBuoy

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I am replacing all the nuts, bolts, washers, etc. on my trailer with stainless. Every old, rusted bolt I have removed, so far, is UNF fine thread. At my ACE hardware, stainless fine thread hardware is quite a bit more expensive than course thread. Does anyone know if there is a compelling reason to replace with fine thread, or will the course thread suffice?
 

JB

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Re: Trailer hardware - course vs. fine

I prefer coarse for those applications, BB.<br /><br />No technical reason, I just prefer it.
 

gspig

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Re: Trailer hardware - course vs. fine

The fine thread is more vibration proof. Course will work OK.
 

Winger Ed.

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Re: Trailer hardware - course vs. fine

Originally posted by BoatBuoy:<br /> Does anyone know if there is a compelling reason to replace with fine thread, or will the course thread suffice?
I use coarse threads & locknuts on hardened or oversized bolts. I never seem to get out on the ragged edge of needing a bolt to be as strong as it possibly can be for its size.<br /><br />But technically:<br />As well as resisting vibration better, fine thread bolts are somewhat stronger for their size.<br /><br />The threads aren't as deep, so you have a larger diameter of steel to resist sheering or breaking than the deeper coarse threaded ones of the same size.
 

Bondo

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Re: Trailer hardware - course vs. fine

Mack Trucks,+ Mercrury Marine, Both Love fine threaded fastners.............<br /><br />Those are the Only 2 places I use them..........<br /><br />The Rest of the World is held together with Course Threaded Bolts................. ;)
 

BoatBuoy

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Re: Trailer hardware - course vs. fine

Well here’s my report. I'd like to thank all for their responses. I’ve finished assembling this trailer and here’s what I learned. I chose to use fine-thread hardware because that’s what the original equipment was. I also chose to use stainless. The original equipment was not, but I’m tired of seeing the rust. If using stainless, don’t use fine-thread fasteners for the following reasons.<br /><br />1. I used nylocks. Original hardware was nuts and lock washers. Nylocks may not have existed in 1955. You will wear your arm off cranking down nylocks on fine-thread bolts.<br /><br />2. Fine-threads are much less tolerant of debris which might find its way into the threads. When that happens, fine-threads cross-thread much more easily. I had that happen once and had to saw the bolt off. Actually, it sawed very easily.<br /><br />3. When using stainless, fine-thread is not necessary because fine-thread is only advantageous when you need the strength fine-thread affords. To quote from boltdepot.com <br /><br />“It is a common misconception that stainless steel is stronger than regular steel. In fact, due to the low carbon content, stainless steel can not be hardened. Therefore when compared with regular steel it is slightly stronger than an un-hardened (grade 2) steel fastener but significantly weaker than hardened steel fasteners.”
 

dingbat

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Re: Trailer hardware - course vs. fine

I also chose to use stainless.
Generaly speaking course thread hardware is used in shear applications and fine thread is used in tension loading.<br /><br />Use losts of anti-seize and hope you never have to dsiassemble or replace any of that hardware. You can't cut SS with a cutting torch and the chances of you getting it apart apart by hand is next to nothing since it so easily gulls. They use zinc coated hardware on trailer for a reason.
 

Scaaty

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Re: Trailer hardware - course vs. fine

Follow what Dingbat just said...NC zinc coated the best. Cheap, grease them up, and the next time around you just torch them off. As a retired Machinist, NF stainless is probably the worst app.....twice the threads to gall, can't torch them, hacksaw will drive ya nuts. SS is tough, but not strong in shear or twist, etc. Just use a touch of blue Loctite if you have vib problems (not red...chemically welds the metal)
 

Scaaty

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Re: Trailer hardware - course vs. fine

Originally posted by Bondo:<br />[QB] Mack Trucks,+ Mercrury Marine, Both Love fine threaded fastners.............<br />Those are the Only 2 places I use them..........<br /><br />Believe it or not, but Harley Davidson has in the past used copious 7/16 NF bolts/and nuts and even 1/4-24 -yes, 24--(NC is 20-NF is 28) in the tappet blocks. Now just where are you going to go for more replacement stuff?
 
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