Classic cars forum & vehicle restoration.

[Uncle Joe]

Both Greeney and I have discovered that the metric bolts fitted to our cars are to a different standard than the current one. I do have a litte info, but not much. Is there anyone that can explain the pre-60 metric system?

As far as I understand things at present, there are 5 different standards at least that could apply to our german/french cars. France has CNM 132 and 133. Germany DIN 13, Switzerland VSM 12002, and the UK (!) BS1095:1943....

Why couldnt they make things in Imperial sizes?

[peter scott]

I believe the pre-war Morris and MG engines used metric threads that are not ISO. This results from Morris buying his engines from Hotchkiss. They also had Whitworth heads to them so that British mechanics could use their normal spanners. The MG parts supplier NTG keeps some stocks of these nuts and bolts.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[ukdave2002]

The Morris 8 engine origins were French, Morris used to use Hotchkiss as an engine supplier and then bought them outright. As a consiquence both engine and gearboxs on 8's and deriviatives right through to the 50's have "metric" threads with BSF/BSW bolt heads the metric threads go back to the 1920's so I have no idea what standard they are.

I wonder how many mechanics over the years have damaged threads on these units by chasing them out with the wrong tap !

[Uncle Joe]

Some of the changes dont really matter, eg if its just a nut and bolt holding two things together. But when there is a bolt that screws into a threaded hole in a plate, the pitch is 0.45mm, and the diameter 2,6 or some other stupid size, then it becomes a nightmare...

[ukdave2002]

Givern the odd / old metric theads in the Morris engine, I have been placing all removed nuts and bolts into labled bags, so they I get it right during reassembly! for ref the coarse threads all seem have a pitch of either 1mm or 1.2mm don't know how that compares with modern metric stuff?

[Uncle Joe]

Metric pitches tend to be a little confusing, as there are both fine and coarse, in much the same way as UNF and UNC. ''Common'' M6 have 1mm pitch, and M8 1,25mm.

However, an early british M6-1,0 or M8-1,25 standard practice manufactured nut will NOT fit a modern M6 or M8 with the same pitch. Standard practice in this country was to use an increased core diameter, which in its turn gives a larger radius at the minor diameter on the screw, and a bigger minor diameter at the nut...

I hope this is clear...doesnt answer my question s though...