About to tackle some exhaust studs holes but wanna ensure I stick to the M10 1.25 rather than drill out and shove some imperial tap in .
There won't be (m)any responses because this is like asking how to weld a soup can lid back onto the can before you put in the refrigerator. Subaru exhaust threads are such an easy, routine repair with a 100% success rate, few people spend time on elaborate options. Many of us repair those in 5 minutesand have no idea how many we've done with zero issues.
Describing the compelling reason to do a simple job differently might be warranted - whatever circumstance is causing the need for an exotic repair might change the preferred style/brand/model/approach.
2. stop into a couple of professional machine shops - after perusing google/Dave's suggestion above - and ask them what options you have, what options you've seen and opinions on the particular ones you like. focus on learning a new tooling or technique rather than just repair your current situation otherwise they'll be in "fix your heads" mode and won't understand why you're asking them to weld a soup can lid back onto the can.
if you have machine shops specializing in industrial, mining, etc locally like some areas do - try those as well even if they don't do automotive work. they may have good suggestions and first hand experience as they're seeing complicated high dollar repairs of machines and equipment. they might not want to talk if you can't/won't be an end customer and the clock is ticking at $120/hour.
3. a machine shop can also make repair inserts. i've had it done for subaru blocks and heads before. they fabricate a plug that threads into the block/head and has a receiving hole the same threads as the original bolt. i've never done it to exhaust studs. have to be sure you have the additional material available to remove to do this. if the hole is made bigger for a more complicated repair - then the internal clearances are being reduced, which may not be ideal. i've taken blown blocks and heads and drilled enormous holes to find the coolant/oil pages behind them and see how much material i've got to work with. not sure exhaust studs go up far enough to get close to cooling passages.
Edited by idosubaru, 18 December 2017 - 11:29 AM.