So my mate reckons that you will never find a 13mm bolt on any Japanese car as 13 is an unlucky number!
I’ve come across 12 and 14 on my MX5 but never a 13.
Wondering if this is true or not. Anyone found a 13mm bolt?
Not a JIS size.
If its about perceived luck, why call one of the Rotaries 13b?
4 is the unlucky number in Japan, because it looks like death,
Assuming you mean the thread size and not the hex head size, M13 is rarely used on anything. Above M6, it’s normally even sizes only.
13mm hex head is normal for M8 bolts, though.
13mm spanner size, so yeah that would be an M8.
Sounding more and more like a myth to me 
Japs have used 12mm head on 8mm thread since the 60’s. Not about luck but all about material cost and weight saving
There aren’t many bolts I haven’t undone at some time or other on at least one of my NA cars, and I only eventually had to buy a 13mm socket after many years to deal with a non-original bolt.
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For some reason, on the NB-FL, the thermostat housing has a single 13mm nut.
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They’ve been known to use an 11mm head on an M8 bolt for motorcycles!
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