R=resistor
E=Shielded 5/8-24 thread
J=14mm, 3/8 reach, 13/16 hex
Same reach as C-10, anything much longer and you are getting pretty close t the top of the head. I have seen people use REL-37 with 1/2 reach, and maybe if I was desperate, but I'd be watching my EGT/CHT pretty close, 'cause I've never tried them (and I don't think they're approved).