I want to make a simple hold down to fit the pritchel hole which is 17mm in diameter. The largest round stock I have is 12mm which seems a little small. Will 12mm work or should I go bigger?
Appreciate your thoughts.

That seems too far from a good fit, you need a fairly close fit for the spring clamping action to grab.

I am using a motorcycle type (like a bicycle chain but heavier) drive chain hooked to a staple on the far side of my anvil stand (stump). I just lay it over the anvil and lift it with my hammer as I slide the hot work under it. The weight of the chain has been all that I need to secure my work but some guys put a board on it to use as a foot pedal for a tighter hold. IMO it is hard to beat this system... it works REALLY well for me!

I made mine with square stock. I had one made from round, but the square rod doesn't seem to slip loose as easily while under preasure. My pritchel is 1/2 inch and I used 3/8 inch square stock.

You can always put a straight piece of stock in the hole and push on it then see if it moves easily. Would take you a few seconds and no need to light a fire.

Phil

Thanks guys. I'll get some larger diameter steel. Also like the sound of using square stock and the bike chain. Might try all of them. Can never have too many tools.

Fold the 12 mm stock over and weld to itself making it 12 x 24mm. Then hammer it down to 17mm round to fit the hardie hole. Put the new larger size stock into the prichel hole and make (bend) the hold down to your specifications.