Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Stub axle thread size

The castlated nut wont go onto the stub axle as the start of the thread looks slightly damaged.

What is the size of the thread ? Iíll need to buy a die to clean it up.

Or a thread restoring file.
David Billington

Thread file is the kiddie for this job. Much easier than getting a die to start on a dinked thread.
Even an ordinary small sharp file used with care, to take down only the actual damaged bits.
Plus a die that size is expensive!

I didnt know there was such a thing. I will have to get one
Thanks :)

A set of standard needle files (small cheap file sets)
will do the job as Greybeard notes.

richard b

I just checked the thread it it looks to be 5/8" UNF which is 18 TPI. The 18TPI thread gauge fitted perfectly.
David Billington


A quick look on ebay show 5/8" UNF dies for less than £10 delivered so potentially cheaper than the restoring file but the restoring file covers 8 thread pitches typically so could be more useful and I as you think the tool for the job. I wouldn't buy the cheap dies if I was planning to use it regularly but for the odd job should be fine.
David Billington

The thread restoring files I have are square and have different threads at each end so one file gives you 8 threads. I have a UNF file (maybe it has UNC at the other end) and a BS/Whitworth file. Money well spent for the very rare occasion you need to use one.

5/8" didn't sound right for the nylocs I used so I looked it up and the nut is - ND607041 - NUT, CASTLE, FULL, 7/16", unless I've missed something again.
Nigel Atkins


As I understand the original question we are talking about the castellated nut on the end of the stub axle and the thread on the end of the stub axle which on mine measures 0.618". Are you thinking of the nut at the top of the kingpin?
David Billington

David you are right and I am wrong, I was the nut thinking of the wrong nut, apologies to all. Too much heat and not enough beer.
Nigel Atkins

Bear in mind that running a die down a thread will remove screw thread material and make the thread looser

If the end is a bit bashed about (arent we all?) just lift away the distortedbit with a needle file and if you can do not actually take the file all the way round

You just need to remove enough distortion to get the nut gripping

If you have another nut of the same pitch a useful dodge is to cut the nut in half down the thread to separate the pieces, clean the edges with a fine file and put both halves of the nut onto the lower, inner and undistorted part of the thread then with the proper size socket simply unwind the reinstated nut from the screw thread with a drop of lubricating oil to ease it along

Do not use a smaller socket unless you want to cut the real part of the thread away
Bill sdgpM

. . . and quick(ish) search confirms your 5/8" UNF.
Nigel Atkins

I had already tried to clean up the thread with a needle file but the nut still wont engage. Its not obvious why. The nut goes onto the other stub axle just fine so its not the nut.

A UNF/UNC thread file is on order, so I'll give it a go with that.

David B. I hadn't realised that dies were available so cheaply. When I've bought them in the past the prices made me wince. Thanks for that.
Bill's cut-in-half nut trick is good. I've done it myself and it works pretty well if the damage isn't too bad.
I have UN and metric thread files, but no BSW/BSF like Daniel's. Now I know where next week's pocket money is going :-)

Don't forget the threads are handed! The LH nut will not go on the RH stub axle, and vice-versa.

Richard Wale

richard you are thinking of the rear axle which has handed threads, both of mine fronts are R/H threads.

M J Pearson

Yep both sides at the front are RH thread.

However I also have to sort the rear hubs out and didnt know they were handed. So thanks :)

Oops - you know what they say about assume?? Makes an 'ass' out of 'u' and 'me'!!

Our Minor has handed 5/8" UNF stub axle threads, which I checked before posting, and the drum braked Sprite/midget uses the same hubs (the disc braked hubs fit as well, we have them on our Minor), so I 'assumed' that the stub axle threads on another BMC product using the same hub, of a similar vintage, would be the same!!


Richard Wale

I was going to post that Richard had done a Nigel but thought it best for others to confirm this first.
Nigel Atkins

This thread was discussed between 20/05/2018 and 21/05/2018

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.