ET-67 lens hood

[Klaidas]

I've ordered a EF 100mm f/2.8 macro USM lens. Now, it has a ET-67 hood as an optional accessory. How useful would that be?
Yes, I know, if for some reason I decide to bang the lens that costs not-so-not-much against a rock, the hood might save the front element, and I will probably be able to eliminate non-image-formatting-light., but... how useful is it really, practically, not just theoretically?

Also, isn't the number part mean to be the same as the size of the filter? *confused* How come the filter is 58mm, but the hood is ET-67?

[Sime]

I have the same lens and the same lens hood... i've never used mine...

[Klaidas]

Also, I was wondering about a tripod collar (is that what the thing that is mounted on the lens in order to be able to mount the lens to the tripod, and not the camera, called?). I have a Canon 400D, and it weighs ~510g, but the lens is, as far as i remember, somewhere around 600g. It wouldn't be too good for the lens mount if the camera was on a tripod and supporting the lens, and not the lens on a tripod supporting the camera that's just hanging there, right?