The usual thing is 20 gauge - .8mm from memory - stainless wire standing about .005in proud of the liner tops. Best used with a shim gasket. My EX500 racebike has used this since it was built in '87. Only downside is you must use a new gasket each time the head comes off as it stretches the shim. We used this setup on the blown 500 too., The head didn't leak at 18lb boost - but the barrel and head moved around on the cases.