M5 nuts and bolts: 8 or 9 mm ATF?

[Dave Erickson]

My collection of M5 nuts and bolts includes some with 8 and some with 9mm heads. Which is correct for 356? When did the standard change?

I assume the 9mm size is correct for a 356, and the DIN standard change that applied was the same one that changed m8 bolts from 14mm ATF to 13mm ATF, and M10 bolts from 17mm ATF to 15mm ATF. However, google searching does not bring up a list of the changes or when they occurred. I think the DIN spec is 137, ao a pointer to the old DIN 137 would be useful.

[Dave Erickson]

I am also having a hard time finding *any* M3 nuts that match the pitch used by Porsche, 3.0x0.6. 3x0.5 is very common, These are the nuts used on original 356A horn grills, and undoubtedly used in other locations. Do any of our vendors sell them? Are they available in Germany?

[Mike Wilson]

I just checked McMaster Carr; only the 0.5. Maybe Belmetric or Metric Multistandard?

Mike

[Andreas Dreher]

The German standard defining metric nuts is DIN 934. In the versions of DIN 934 of March 1961 and before, the M5 nuts are listed with an ATF of 9 mm, the M8 nuts with an ATF of 14 mm. The next version was published in March 1963, where the M5 nuts are listed with a 8 mm ATF, and the M8 nuts with an ATF of 13 mm. The 1963 standard also stated (my translation): "Until April 1, 1965, hexagon nuts with the thread M5 may still be delivered with an ATF of 9 mm, and the heaxagon nuts with thread M8 or M8x1 may still be delivered with an ATF of 14 mm."

On M3 nuts, I found that many times I thought I'm dealing with M3 threads, they were actually M3.5x0.6 threads. M3.5x0.6 nuts are available at McMasters; might be worth a try.

[Dave Erickson]

Mike, thanks for the suggestion. Belmetric has M3x0.6 nuts. They list them as 'Retired". https://belmetric.com/extra-coarse-reti ... bon-steel/? I ordered some, $0.17 each.

Andreas, thank you. That is very useful information. My Conv. D definitely uses the earlier version of the standard. I don't know whether Porsche used M3 or M3.5 The nuts Porsche used were 6mm ATF.

[Andreas Dreher]

In the '61 and earlier standards, M3 nuts are specified with 5.5 mm ATF, M 3.5 with 6 mm ATF.

[Dave Erickson]

M3.5 it is then. I noticed when I ran an M3x0.6 tap through the nuts I have that the tap was a loose fit.