Hollowtech II LH lock spacer

[02GF74]

As per title, what does this small spacer (1 mm thick) do?

And what would happen if it is missing?

When the bolts are done up quite tight, the gap in the crank is still big enough for the spacer to move so I don't think it is there to stop overtightening the crank.

It has a tiny pin, not easily seen in picture that I can't figure out the purpose.

Part 9 in orange below

 

[Fattman]

I believe it is a belt-and-braces bit which will stop the crank arm sliding off if the bolts have worked a bit loose. It's always seemed a little odd to me, disconcerting how it sort of wibbles around - just makes me want to get those bolts nice and tight with a bit of threadlock on them...

 

[Gerry Attrick]

I suspect that in the past, probably in the good 'ole US of A, that someone has tightened them incorrectly, a crank has parted company with the BB and the rider been dashed to the ground resulting in the usual rush of vultures lawyers suing the backside off the makers/retailer and their dogs. Result, manufacturer has no choice but to take on what is rightly the customer or mechanic's responsibility.