M10X1.25 straight machine thread. Fumoto F124N which has the 3/8" hose adapter/nipple. I think I paid about $20. No adapter was needed, as you can see from the picture of mine on the front of engine. My engine (and the kick starter adapter plate) are adjusted "up" forward, so you may/may not need to... A) move engine plate forward to install/screw it in, or B) grind back a little on engine mounting plate as needed for clearance like I did before I installed my kick start as seen in pic. You could also install it on the rearward oil drain plug, which would work just as well, and would involve no grinding/clearance problems at all, once the valve is "installed/screwed in", if you have the "kick starter plate" under it, which acts as a 1/4" "shim", thus keeping it up and above the motor mount plate. It'd just be a little less convenient getting a finger on the lever to open/close the valve. (see pic) If I didn't have "ground clearance" issues on my ZR7 and HHR, I'd have these on them also. Since they don't use an oil filter, and only holding 1 pint, frequent oil changes are a must, since it's now so cheap and easy. (1qt of 10W/30 full synthetic at Fleet is $3)
