14mm on M8 is quite common but don't know why, maybe so all the old fogeys with 9/16 spanners like that size

the 8.8 is a strength designation. The reason for having different sized nuts is because a normal spanner set does not include two 13mm spanners. So if you want a spanner at each end to tighten it it is extremely helpful to have different sizes. The same is found occasionally in imperial bolts on cars that have been designed by someone who actually does his own servicing.

The sensible reason for the bolt head being a different size to the nut is so that only one set of spanners need be used for maintenance. Nuts usually get damaged, so replaced more often than the bolt, so they are the standard size and the bolt head is sensibly one size larger.

If you want odd bolts, try working on pre-war French cars! They made up their own sizes and pitches!

.

Assuming that you were quadridextrous

… one-man-band ?

MichaelG.

Edited By Michael Gilligan on 31/03/2019 23:36:41

Hi 13mm for an 8mm bolt is only a standard. I've seen 8mm bolts with 14mm heads a number of times and I've even come across them with a 12mm heads. Other standard sizes also have variables, like 12mm with 18mm heads, 10mm with 16mm heads. It is often due to their usage for a manufacture to which size heads are used and often down to cost if you produce equipment using many thousands of bolts per year.

Regards Nick.

Apparently, 14 mm A/F was an old DIN standard, but they are still available

It doesn't work quite like that. Most of the work done turning the spanner goes into friction between the male and female thread and the face of the head against the abutment. This is why torque settings on bolts aren't that reliable, change the friction coefficient and you change the clamping load. Finer threads are more affected as the rotation for a given axial movement is more.

I did say friction conditions, for that very reason!

Often torque settings are qualified by specifying the lubrication, or otherwise of the fastener and its threads. Presumably after having investigated the results from a particular combination of materials and lubrication.

If you want to know the clamp load applied, use a load cell, strain gauge the components being clamped, or after some experimentation, tighten the bolt to give a known extension.

Forgot to mention Pilgrim nuts for large fasteners!

The ultimate is probably tightening until the fastener just goes into yield, and takes a small, permanent extension.

This is a most efficient use of a fastener, and should produce consistent tensile loads.

I found that W range fasteners, into cast iron, would give consistent results, lubricated with soluble oil (Which we deliberately varied between 5 and 20% concentrations ).

For a variety of reasons, it took six months before simultaneous yield tightening of 32 fasteners was considered safe to be allowed in high volume production. Thereafter problems were almost unknown, and gasket failures dropped to zero.

Howard

Edited By Howard Lewis on 27/09/2023 16:54:17

The taper is the draft angle of the forging, to allow the product to be removed from the die, for the same reason that castings have a draft angle on internal and external faces.

Because of the age of the design (1947 saw the ML7 launched ) the fastener on the Myford is likely to be a BSF size. The stud for the front too[post is 7/16 BSF, from memory, so ithe rear one is likely to be something similar with a Whit form thread.

Howard

Edited By Howard Lewis on 29/09/2023 21:55:43