Is there any risk in drilling out the thread in my 300 f/2.8 tripod mount from 1/4 to 3/8 inch? Or is that overkill? I'm concerned that the 1/4 inch bolt might snap off when toting it on a monopod over my shoulder.

I carry my 300/2.8 IS on a 'pod over my shoulder, never had a problem, though I always make the sure the monopod is tightened up properly.

On a 300? I think it's overkill. Now the 600 f/4 IS, that's a different story.

Seth Tower wrote:
On a 300? I think it's overkill. Now the 600 f/4 IS, that's a different story.

True the 600/4 IS is much heavier but that uses the 3/8 bolt for a monopod or both the 3/4 and 1/4 bolts if connecting via a lens plate to something like a Wimberley.

Change your bolt from a normal bolt to a class 7 or 8 one. Available from www.mcmaster.com put in this part number 92423A539 which is a 1/4-20 X 1.00 inch long cap screw made from A286 high strength steel (Nasa certified bolt). Do NOT buy bolts from Home Depot / Lowes / etc ...