my kingdom for a decent one had loads, get above 250amps and they all melt, lincoln do a clamp type one but its a fiddly little sod to use, try ed a magnetic one the rep said it was good, worst one yet...... Im open to suggestions.
have a look here http://www.johndavies.co.uk/nwcables.htm
shows you most of the types available.
But if you have a local BOC tradequip, you won't go far wrong, as Paul says.
The very first modification to my Clarke Mig, was to chop the crudy clamp off and lob it in the bin. It was poor quality and often had sparks of the contacts.. upgraded to a copper contact 200a proof clamp, much better.
Lowest hassle option would be send a PM to weldequip so sort out something decent. Though before I took the easy route I bought a clamp for my Clarke from Axminxter Tools in the UK. They've stopped doing my clamp, but they still do others that look half sensible.
They are easy to swap. Chop off the old clamp, expose half an inch of strands, and bolt them into the new clamp. Non corrosive (copper or brass) clamps with some decent clamping force (big spring or screw clamping) with a large clamping area are the best. And they can make a big difference over those rubbish crocodile clip clamps.
When connecting the earth cable to the clamp, it is always best to terminate the cable with a lug (bolt on / hammer on / crimped) which is then bolted to the earth clamp. We have found if you just try to trap the cable under the bolt with a washer perhaps, or other such methods, in use, the cable will get very hot at this point, melting the sheath, weakening the joint, reduced welding performance etc. I presume this is due to increased resistance in the wire as the csa is effectivly reduced. It is suprising how a good earth will improve the results you achieve.
Yes, crimped is best. If you solder it it will have a good connection but the wires will break off over time. A crimped lug allows the wires to flex a bit.