Has anybody used 12 pt. reduced-dimension nuts on their exhaust
flanges? I was surprised that they were even available with course
threads, but <a
href=
"http://www.summitracing.com/parts/arp-401-8303/overview/">Summit
Racing</a> carries them in stainless steel with coarse threads
(photo at link). I ordered 8 of these today which I intend to use on
my exhaust flanges. They take a 3/8" wrench which I am confident
will have enough clearance to be able to get back behind the exhaust
pipe where a 1/2" wrench won't fit. These are
not lock-nuts
so I'll still use a split lock washer underneath. Any comments on
this plan would be appreciated
I also switched to 12-point reduced diameter "K-nuts" for my Lycoming exhaust.
However, I would strongly advise against using stainless steel. It will gall and weld to the stud, then the stud will come out with the nut. If you're lucky. If not so lucky, the stud will break off.
I used a black-oxide chrome-moly steel flange locknut from the aviation department at McMaster Carr.
Part Number 90759A200
Chrome-Moly Alloy Steel 12-Point Flange Nut, Black-Oxide, 5/16"-18 Thread Size
Before I switched to the 12-point nuts, I used a 1/4 drive socket ground down to fit into the space. the socket depth was cut down so that it just engaged the top 1/8" of the 1/2" hex nut.
BTW "standard" 5/16-18 hex nuts fit a 1/2" wrench. If your nuts need a 9/16" wrench, they are "heavy" nuts.