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Ebay - Buyer beware

b'knighted

Well Known and Active Forum Website User
VOC Member
I saw this item on ebay and was quite interested until I noticed that this is a set of UNC screws.

Ebay item 370678265113
"Vincent Comet Engine & Gearbox Covers Stainless UNC Allen Bolt Screw Kit BURMAN
Item specifics

Condition: New: A brand-new, unused, unopened and undamaged item in original retail packaging (where packaging is ... Read more about the condition
Manufacturer: Vincent
Model/ Series: Comet
Vincent Comet 500cc Singles Engine Covers Stainless Allen Screw Kit
Total 42 Stainless UNC Socket Capscrews & nuts. The factory original fasteners were cadmium plated slotted cheese head screws
Includes gearbox cover nuts for BURMAN gearbox"

I contacted the seller suggesting that Vincents will have British threads and fitting UNC may cause damage - This was his response:

Kit listed at request of the first buyer who is delighted with item. plus, FYI no lesser person than Glyn Johnson (VOC builder) was instrumental in developing and approving the Comet and Twins kits with us, and has reported no issues "Forcing" UNC screws into BSW holes. I suggest you contact him to check this statement if you dont believe me, and in anycase you don;t have to buy the kit. All the information necessary is contained in the listing, which I recommend people READ before they buy regardless of item (we dont bury important info in fine print). These are Allen bolts NOT cad-cheese, so owners should be alert that they are risking the scorn of their snooty peers by tampering with what God himself hath ordained.
- stigfasteners

I wouldn't want to use them but you can make your own minds up.
 

Albervin

Well Known and Active Forum Website User
VOC Member
A quick search threw this up (cut and paste follows):
BSW and UNC threads are compatible except for 1/2" diameter. BSW, also known as Whitworth, is a British thread standard devised in the 19th century. UNC or unified course thread is an American thread standard and is very widely used. Examples: 1/4BSW and 1/4UNC threaded fasteners are interchangeable, as are 5/16BSW and 5/16UNC threaded fasteners. A 1/4BSW nut fits a 1/4UNC bolt and 1/4UNC nut fits a 1/4BSW bolt. The sizes that we get asked about the most and which cause the most confusion are 3/16BSW and 10-24UNC. The UNC standard uses gauge sizes to denote diameters of less than 1/4" in diameter. 10-24UNC is one of these sizes. A 10-24UNC fastener has a diameter of 10 gauge and has 24 threads per inch. The good news is 3/16BSW and 10-24UNC threads are equivalent and interchangeable. Note a couple of things. [1] 1/2BSW and 1/2UNC are not equivalent and are not interchangeable. You must match 1/2UNC nuts with 1/2UNC bolts and screws. Similarly 1/2BSW nuts must be matched with 1/2BSW ...

Why would you consider this alternative when the real deal is available from VOCS or Russell? I don't know if Glyn reads this forum but a reply from him would be enlightening. The arrogance, condescension and petulance of the seller's reply would drive me away in an instant.
 

A_HRD

Well Known and Active Forum Website User
VOC Member
The UNC threads have a 60 degree flank angle as opposed to the BSW that have 55 degrees. Also, the crests and valleys of the threads are different, the BSW having more rounded radii. But the pitch (tpi) is the same (except 1/2").

So, yes they are different; but UNC bolts will fit effortlessly into 60 year old worn crank cases, because the thread differences are only slight. This may wear your precious crankcase threads a little more as the bolts are tightened, but you pays your money and takes your choice.

Personally, I don't like to see allen headed screws on Vincents any more than I do modern carbs, alternators, etc. But everyone is entitled to their own preferences.....

Peter B
Bristol, UK
 

clevtrev

Well Known and Active Forum Website User
VOC Member
If anyone thinks they still have 1/4" whit threads in their cases, I suggest you get a plug gauge and try them out.

Just done a few calculations. the only place where the UNC thread will foul the Whit thread is at a point near the crest.
The amount...... .0007"
The effective difference between the two is .001" . So after sixty years of assembling and dismantling, in an aluminium housing, the whit form will have partly disappeared. So absolutely no problem with using UNC where the pitches match.
 
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Albervin

Well Known and Active Forum Website User
VOC Member
If anyone thinks they still have 1/4" whit threads in their cases, I suggest you get a plug gauge and try them out.

A friend has just "reconditioned" his 1947 Rapide. Original screws, original cables, original! Ok, it wasn't pretty BUT I think the paint was/is original too.
 

Len Matthews

Well Known and Active Forum Website User
VOC Member
I got a set of screws for a Twin engine from Stig Fasteners and was well pleased especially when I found they came with three Allen keys and a sachet of barrier grease. The only problem,as with most cap head screws, is that the O/D of the head of the 3/16"s ones are too large for the counterbores in the ATD Inspection cover.
 

vince998

Well Known and Active Forum Website User
VOC Member
Are the BSF wire thread inserts really 55°, or more likely mass produced 60° (for UNC?)
I believe they are made by coiling square(ish) section wire?
 

nkt267

Well Known and Active Forum Website User
VOC Member
I believe they are made by coiling square(ish) section wire?
More like a diamond shape. Exterior to match the oversize insert tap which is marked with the appropriate thread size, so i would assume that the interior is correct for the marked thread form. I have sets of Whitworth,Cycle,Metric and Unf.John
 
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