AN19
STANDARD LOCKNUT AN19 3.73-12" THREAD SIZE, 4-15/16" OD, 4.563" FACE DIA.
You will find that the stainless steel parts are non-reactive with acidic substances.
Schiebel - Austria Mine Detecting Set AN-19/2 6665-21-906-1023
I’ve seen RRG gear in many factories because it holds up to abuse.