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Sourcing a Bolt

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William Harvey 118/07/2021 10:37:29
120 forum posts

Hi all. Looking for some imperial screws to rebuild a gearbox.

Size is 5/16” x 7/8 and 5/16” x 1”.

Gearbox is aluminium so I think I need zinc plated bolts not stainless?


Brian H18/07/2021 10:42:03
2214 forum posts
113 photos

Can you indicate what thread and head type. I know that doesn't answer your question but it may help to locate some screws. (It also helps to push your query back to the top of the list!)


William Harvey 118/07/2021 10:43:09
120 forum posts

Sorry UNC

Andrew Tinsley18/07/2021 10:50:30
1461 forum posts

Plenty of fixing suppliers. I use Spalding Fasteners and Bolt Base, they both have a usually quick turnaround.


J Hancock18/07/2021 10:53:29
699 forum posts

Zinc/Aluminium/Steel , too many metals , stainless bolts for me.

not done it yet18/07/2021 11:34:21
6282 forum posts
20 photos

I have had good service from

GWR Fasteners Limited

Jude Robinson

Units 6-7 Artillery Business Park

Garrison Avenue, Park Hall,



SY11 4AD

United Kingdom


They have an e-bay shop. Good, fast, service. I’ve used them several times.

colin vercoe18/07/2021 12:23:28
59 forum posts

stainless in aluminium can cause the aluminium to corrode away especially if subject to wet and salt etc, if you use stainless you should also use nylon isolation washers.

MadMike18/07/2021 14:34:12
223 forum posts
4 photos

A couple of points regarding the use of stailless steel and aluminium if I may.

There is a theoretical risk of corrosion occurring due to the reaction caused when using dissimilar metals. This is easily solved by applying Copper seal to the threads.

No doubt you have all seen those large glazed facades on offices, shops and shopping malls, plus all of those glazed roofs roofs on many commercial buildings. Well, as somebody who was involved in manufacturing and installing many such projects, I can tell you that without exception the corner joints, fixings and component fasteners are just about 99% stainless steel screwed into the aluminium extrusions which themselves have screw ports extruded into the profiles. I am not aware of any such assemblies failing due to the mix of stainless and aluminium.

Remember also that many boats are aluminium hulled and their fasteners and even the topside fittings are very commonly also stainless steel. Again I know of no failures due to this.

I use stainless steel fasteners on all exposed areas of my restored motorbikes and into the aluminium engine casings and once again no failures in almost 60 years. I hope this helps in this debate.

Robert Atkinson 218/07/2021 15:54:28
1073 forum posts
20 photos

For a steel fastner in aluminium alloy the best finish is cadmium plated. However these are no longer allowed because cadmium is toxic. (you might find NOS aircraft ones of the right size on ebay)
Next best is passivated zinc plated. Most stainless steels will cause corrosion in light alloy in the presense of moisture as will copper. Using "copper slip" only helps because of the grease content. If you must use SS in aluminium alloy then Duralac (yellow or green) is better choice to limit corrosion.

This is not my personal opinion, it's decades of experience in the aerospace industry....

Robert G8RPI.

William Harvey 118/07/2021 17:40:10
120 forum posts

These bolts are for the retainer plate that holds in one of the main bearings of the main shaft in an A Series Gearbox, so no moisture just lots of oil.

Howard Lewis18/07/2021 18:45:13
5237 forum posts
13 photos

If you had said 5/16 UNF x 1, I have hordes!

If all else fails, you could make some!


Jim Smith 818/07/2021 18:56:39
29 forum posts
8 photos

I've had plated bolts into cast ali on motorbikes where the (zinc/ali?) plating has rusted out causing threads to collapse when removing bolts. Chinese A2 stainless bolts are normally sold degreased and using them out of the packet causes problems. I use CopperEase grease on new stainless bolts and haven't seen corrosion or thread damage yet.

Robert Atkinson 218/07/2021 19:03:19
1073 forum posts
20 photos


Edited By Robert Atkinson 2 on 18/07/2021 19:15:55

Nigel Graham 221/07/2021 23:26:52
1676 forum posts
20 photos

Stainless-steel and aluminium-alloy can be a bad combination depending on the individual grades and the environmental conditions.

The alloys for marine use should be ones developed for the role. I have seen an assembly that had spent some time in the sea, in its intended use, whose stainless-steel thread inserts sat all smug and bright in craters filled with white sludge, in the aluminium end-plates.

I can't see it being a problem in something that is drenched in oil; but it certainly can be with any water about.

A non-metallic grease - mineral, silicone or petroleum-jelly - may be better than a copper-based anti-sieze compound.

I used to test experimental assemblies made typically from "ordinary" aluminium-alloy (HE30 - I don't know its modern moniker) held together with A2 or A4 grade stainless fastenings. Despite their designers' touching faith in anodising, the test-pieces' necessary immersion in a tank of fresh water kept sweet with only normal swimming-pool filters and additives soon started things fizzing.

I wonder if this could also be a problem for miniature railways using stainless-steel bolts with aluminium rails. It might not if the joints are always above the ballast and kept clean, but may be if vegetation or soil accumulates around the track.

Howard Lewis22/07/2021 09:10:58
5237 forum posts
13 photos

A marine environment will be hard on any material, because the saline atmosphere, allied to moisture produces an electrolyte. Consequently some corrosion is likely to take place.

ONCE, we fitted copper / asbestos gaskets to a marine engine, between a cast iron head and a cast aluminium exhaust manifold. NEVER again! You could almost see the Aluminium fizz!

In an oily environment, which will exclude moisture, electrolytic action will be absolutely minimal. probably the best for any combination of metals (As long as the oil does not contain reactive elements, like some EP oils )


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