.035 with the 69 ignition.if you use msd or something equivalent it will increase to .045 or even .060.if you have the 69 stock ignition and like free h.p. cut your ground strap back on the plug end.its worth 10 h.p. and works.you will have to replace the plug more often but they're cheap. www.edelbrock.com/automotive/sparkplugs.html
check out "cut back ground electrode,jc4 type."