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MG MG Y Type - Round Headed Front Seat Fixing Bolts

The above fasteners on YB0952 are threaded 1/4-20 UNC. They appear to be original. The self locking nuts fitted to them also appear to be original. They do not have the "locking" portion made from white nylon as is common today. It more resembles the material used on the red fiber washers fitted to the carbs and radiators on our cars. I do not recall finding any other UNC fasteners on this car.

Have other cars been found fitted with the same fasteners in this location? Were self locking nuts of this design uncommon, or unavailable, in BSF sizes at the time our cars were manufactured?

A small point of originality, but your experience is requested.
RC von Dullen

Hey Rocky

Can you post a picture please as I am completely at a loss as to what you are referring to?


Paul Barrow


My apologies for my inability to express myself in an understandable manner.

I will try to post a photo of the fastener I reference by tomorrow. The bolt is 1 3/8" long X 1/4" diameter. I measure the nut as fitting a 7/16" AMERICAN wrench.

In the interim, you may find a photo of these parts as number J376 on the NTG web site:

These bolts are also described by David Lawrence in LTBY Ch 12 Sec 7.a Front Seats, pg 181 of the 1997 first edition.

They are further discussed in the article "Seat Bolt Gaps" in the HINTS & TIPS section of your website.

Again, I apologize for any confusion I have caused you and hope you, or your readers, can assist in answering my questions.

RC von Dullen

Hi Rocky

Great link and that is what I thought you were asking about - just wanted to be sure.

My GUESS (and it is only that as it has been a long time since the late 1940s - early 1950s) is that the material is basic thread lock material but whether it was original or not ... who knows :)!

While it is great to strive for originality there are somethings it isnt too worthwhile chasing. I have to admit that I have absolutely no idea about the commonality of the material as I only got into cars in the 1980s. My guess though is that on components like this where vibration loosening could be a problem it was more typical for manufacturers in the 1950s to either use wire fastenings through castle nuts or else the use of shake-proof washers.

Maybe someone else knows??

Paul Barrow


Here is a photo of the seat runner nut and bolt from YB0952.


RC von Dullen

Many thanks Rocky - still no idea on the red stuff though :)

Anyone else any ideas please?

Paul Barrow

Hi, from the pic, they look to be identical to mine and thus probably original.

The nut shown is a common forbear of the modern nyloc stiff nut but as suspected, using a hard fibre. This type of nut was known pre WWII, as it is illustrated in a 1930's "machinery handbook" as is the "Aerolock" nut a stiff nut reliant on the distortion of the top threads (still available today) the caveat being they are both single use, unlike the nylock which can be reused.

Not sure if the fibre inset types are available now, but for the sake of originality I would be tempted to re-use but with a spot of modern thread locking liquid.

HTH Dave
D P Jones

This thread was discussed between 20/03/2017 and 22/03/2017

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