I have one of these:
https://www.mcmaster.com/#6669k11/=1b4na5c
... somewhere... seem to have lost it ... somewhere.... couldn't find it when i originally posted or now, so,
OUCH! it was spendy. i bet it is just hiding under some other project
but i used it tens or dozens of times
I have the same tool referenced by crassius, mine is made by koch, it is new in the blister pack. one thing i like about it is it seemsto have roller chain as a component part.
I think a chain breaker is a core tool to the hobby, 15 bucks is reasonable, in my opinion,but i have a lot of tools.
weirdly, i found a clamp much like reference by enceladus, but mine is cast material. i may make one just because i like to make tools.
Bairdco, that is good to know and i may have missed that in the spec sheet- thanks for letting us know because i may have bought one. - Though if i need to make a pin or shaft smaller, i usually chuck it up in my drill. Then using the drill like a lathe use a file or grinder, it gives a surprisingly uniform finish.
While i m thinking about it- get a good bike chain tool too. truthfully, i have come to consider them disposable, and buy several cheap ones to keep one on hand for when they fail.