[prkaye]

Anybody know a part number for an all-metal locknut for AN4 bolts (for use in the engine compartment)?

 

[apkp777]

MS21042-L04 or AN363-428

 

[Stevea]

Use either an AN363-428 or MS21042-4.

http://www.aircraftspruce.com/catalog/hapages/an363.php

 

[apkp777]

I like the MS21042s. They have a reduced size and aren't prone to rust as are the 363s.