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MG Midget and Sprite Technical - Diff drain plug

I tried to drain the differential on my 77 midget last weekend, only to find the plug is something like a 7/16" square bit. Can't find one at my local parts and tools shops.

Am I right on the tool? Seems odd. I checked the archive, where it was suggested that one grinds off a 1/2" socket driver. Is this really the way to go?


jf Falconer

The problem is John that it is tapered. In the past I have used a square drive from a 3/8th socket set with good effect but grinding a 1/2 inch would probably be better. Occassionally I have been unable to get it out no matter what and I have resorted to this method
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Bob Turbo Midget England

Excellent, Bob.

This may justify that welder I've been wanting!

Thanks for the point about the tapering. This will guide my grinding, which I may try first.


jf Falconer

Recently had the same problem, but I was able to remove the plug with a pair of Vice Grips...ordered 2 new ones from Vic Brit ($2.95 each) & they came with a 3/8" square hole.

Much easier to remove now with a standard 3/8 drive ratchet.
Dave Rhine ('78 1500)

I've also used the 3/8" drive from my socket set.

Gryf Ketcherside

the diff plugs are a pain, but once you get it out, you can replace it with a standard plumbing plug. The ones i used still have a square grip, but is easier to manage because it is a positive rather than a negative. That is there is a little square post that extends from the back of the plug which you can easily grip with a pair of vice grips rather than a hole you have to find something to fit into.

i don't recall the size plug i used but i just took my diff plug with me to the home improvement store and compared. (this is my normal means of matching hardware, since i don't trust myself to remember sizes/threads correctly).

Chris Edwards

Bob - that's how I'd do it. I have an allen-key plug on the bottom of the diff now - not so easy to align with the trolley jack, though!

Anthony Cutler

I use an old bolt that I have adapted to fit. I forget the size - but it has a 3/4" hex head and is cut down to about 1" in length. I have ground flats on the bolt shaft to form a slightly tapered square that fits neatly into the drain plug. It then undoes with a socket or open ended spanner. Simple and quick to make once and it lives in the bottom of my tool box.

Guy Weller


I needed a tool for this years ago and bent a piece of IIRC 12mm square black steel bar then ground the end with an angle grinder to suit the plug socket. Still kicking around in my miscellaneous tools draw.
David Billington

of course if you run out of scrap, or time to faff about, you can always use the right tool for the job...

David Smith

David, aperently we are the only non-bodgers here. :)

Thats part of the fun of owning a spridget: collecting the right toles over the years.

Arie de Best

David and Arie: Good grief! First time I've ever seen a tool like that! For the pros, right?
JM Morris

JM, im deffenetly no pro, David on the otherhand is a racer so he could be seen as a pro. :)

Its not expensive but very handy when you have one.
I have more of these tools that most people have no clue what its for.
Its part of the fun collecting weird but usefull tools over the years.

How about this one:

Arie de Best

that looks like a door weatherstrip installing tool.

Norm Kerr

OK I'll see your weatherstrip tool, and raise you - a what?

David Smith

clue: it's not just for Spridgets
here's a close-up

David Smith

pipe cleaner, or something from ann summers?
d cusworth

battery terminal cleaning brush

nice one too David, no plastic junk
bill sdgpm

I knew that one, but David beat me to it!
Chris Edwards

When I was about 12 or 13 I worked Saturdays in a garage and used the money to buy quality tools. Still have and use most of them (except for the small 'toy' spanner sizes that my kids couldn't resist). I bought one of those drain plug tools because 'real' mechanics had them in their toolboxes. Used it maybe three times in 30 years, and now have used it 30 times in the last 3 years!
Mike Allen

LOL!!! I love you guys! More! (I've got the battery terminal cleaning brush). There ought to be a separate thread for this--"weird and rare but useful tools" or some such.

Y'all crack me up!
JM Morris

LOL!!! I love you guys! More! (I've got the battery terminal cleaning brush). There ought to be a separate thread for this--"weird and rare but useful tools"
JM Morris

are the hardware plug threads the same as the diff plug ones or are they "just close"? I seem to remember some Brit threads were very close , but not exactly the same. Something like 27 TPI as opposed to 28 TPI.Might they jam in and seal OK but not be correct? There are so few threads involved in this case that being off by one might work especially if dealing with brass. It might screw in and feel a little tight but a twist of the spanner would make it seem alright.Just a thought,-- I am not on a crusade on this matter!! Bob C in Kansas USA


chamberlain Bob

"Chamberlain Bob"

You are correct mate the casing of the Spridget diff I believe is actually 3/8th BSP which is 18 TPI whilst the pipe fittings we now use in Britain are 3/8th NPTT (National Pipe Thread tapered) these are 19 TPI not a significant difference in this application but enough to feel it when screwing in. However it will screw in and seal (rightly or wrongly?)
Bob Turbo Midget England


I think you're incorrect there about us now using NPT in the UK, still BSP in all the standard stuff that I come across unless it's made in the US. BTW the ISO gas/pipe threads are based on BSP so I would suspect worldwide more pipe is compatible with BSP than NPT. Apart from NPT and BSP differing by 1 TPI typically there is the thread angle of 55 degrees for BSP and 60 degrees for NPT.
David Billington

I always use a bit of red Hemetite on the threads as an extra sealer. And am then careful not to overtighten. It seems to me that a tapered thread has the potential to exert a tremendous radial pressure on the casing with the multiplier of thread pitch and the taper which I suspect could crack a housing if one was too agricultural with it.

Guy Weller

This thread was discussed between 17/05/2010 and 19/05/2010

MG Midget and Sprite Technical index

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