Practically Classics Forum

Hi folks, i need some help identifying the type and size of an imperial nut. I don't have any thread guages. I am greatly confused by all the different standards. What would one need to know to tell what type and size I should source as a replacement?
Thanks in advance for your help.

First thing IMHO is to determine whether it's an AF (Across Flats) standard, or one of the other standards such as Whitworth etc.

If it's AF, the easiest way to tell is to see if an AF spanner fits it perfectly - there's only ones size (1/2" IIRC??) that's pretty much exactly the same as a whitworth, of all the other sizes it will be clear that the spanner isn't fitting properly.

If it's AF, then the threads normally come in two standard flavours: UNC (Unified Course) and UNF (Unified Fine) - I'm not sure what the TPI (Threads Per Inch) are for these, but they are fairly obvious - most threads on a car are UNF.

Hope that helps a bit?

If you can tell us what it's from or what it's for, then we may be able to tell you just from the application.

Cheers!

Thanks Luxobarge,
It's off an old gang mower. I'll try to get a photo and check which spanners fit well. Thread doesn't appear to be particularly fine or coarse. It's probably near-ish to M16 metric sizes. I'll measure it all and provide some more useful info.
Paul.

GIYF http://en.wikipedia.org/wiki/Unified_Thread_Standard or http://en.wikipedia.org/wiki/British_Standard_Whitworth

As Luxo says, UNC and Whit go by threads per inch, so a ruler is all you need!

UNC and Whit are very similar (the thread angle is different - though pitch is the same and UNC nuts will run on Whit bolts and vice versa for all popular sizes apart from 1/2"). 5/8 UNC is very close to M16 and almost tbe same as 5/8" Whitworth (I think - BSF and Whit threads are measured differently and I can't remember which is measured at the "bolt diameter" !). So much so that I have one or two spoilt M16 or 5/8" UNC nuts (I can't remember which one is smaller but the TPI/pitch is almost the same)

My favourite online supplier (Namrick) for smaller bolts only go to 1/2" but I can usually get 5/8" UNC on eBay without problems. There's a long and boring story there about buying two packs of five 5/8 UNC bolts and later realising I only needed four - and that I already had plenty of the length required. (if you need 2" or 3" x 5/8 send PM with your address )

There's a strong chance that an older mower will be Whitworth, though the old BS sizes were supposed to be obsolete by the mid 70s. My early 50's rotovator uses BS sizes, though there are now some UNC nuts and bolts here and there.

I have no idea how you all manage to remember that much detail! I just rummage through my box of bolts until I find one that fits :S

TerryG wrote:I have no idea how you all manage to remember that much detail! I just rummage through my box of bolts until I find one that fits :S

Lol! That's exactly what I did for many years, and still do quite often. However, when I came to restore my Midget I decided to replace most of the nuts, bolts & washers with stainless steel, so because I had to order them, I had to get into understanding what sizes and threads they were - that's why I'm up to speed on AF sizes (used almost universally on the Midget) and a bit more hazy on Whitworth, though the Morris Minor irritatingly uses lots of Whitworth, but I haven't had to replace many yet.

Unfurtunately indeed an old lawnmower is quite likely to use Whitworth - see if your AF spanners fit and if they don't then that's the most probable size, and take it from there.

Just a thought - if you can narrow it down and it does turn out to be a whitworth size, there's every possibility that the same nut features somewhere on a Moggie, so lots of spares suppliers out there will hold them!

Cheers!

My excuse is that I'm a boring old f*rt! Though I did have to manage a large stock of bolts when I worked as a storeman for a farm machinery dealers. There's nowt that gives you more encouragement to learn than angry farmer!

As Luxo says, when you have to work with them, you soon learn to spot the size, thread pitch etc, though when I get to 1" (or 25mm) or larger, I still have to measure up - they were somewhat less common (though 9/16 UNF or UNC were pretty rare too!). TBH, I hate working on the Golf - all metric and I never sold fine thread metric stuff! Luckily, I haven't done anything with the current Golf - yet!

To make things really entertaining, the tractors' track rod ends use BSC threads! That's British Standard Cycle and it took me ages to work that one out when I had to recut the "nuts"!

TerryG wrote:I have no idea how you all manage to remember that much detail! I just rummage through my box of bolts until I find one that fits :S

Same for me Terry, but my box of "things that will come in handy one day" failed to deliver this time.

Thanks all for your input. I'll let you know what I discover with my ruler, sockets and calipers.

No one mentioned BSF.!! i work with BSF day in day out on my engines and a fair bit of BSP.