PJ-068
 GENERAL AVIATION MIC PLUG
 This is the plug that many pilots have trouble finding, that's because it's only used in aviation. The mating
shaft of the plug is 5.23mm or 0.206" or as a fraction
it's somewhere between 13/64" & 7/32". The one
shown is to Mil: M642/5-1,   NSN:5935-00-636-6602

PJ-055
 GENERAL AVIATION EARPHONE PLUG
  The mating shaft of the plug is 6.35mm or 0.250"
or  as a fraction 1/4".The one shown is to
Mil:M642/4-1, NSN:5935-00-192-4760.
You can buy a plug with similar mating
requirements at just about any electronics store.

U-174/U (TP-101)
 HELICOPTER HEADSET / HELMET PLUG
  This is a NEXUS plug, not a NATO plug
(sometimes referred to as a US NATO plug)
and it is not compatible with the UK NATO
plug below. Wiring,
 Tip(1) Mic low (2) Ear high (3) Mic high (4) Ear low

TP-120 & TP-120B
 HELICOPTER HEADSET / HELMET PLUG
   The TP-120 & 120B are industrial equivalents to the
U-174/U, TP-101 and in the general aviation area is
more than adequate. Gray is standard and the "B"
denotes a black back shell. The strain relief is also different.

PLUG 671
 UK or EUROPEAN NATO PLUG
  This plug will not mate with the Nexus range, the
mating shaft diameter is 0.43 mm bigger. This is a
Mil spec brass plug, NSN:5935-99-946-6652. Wiring,
Tip Mic, Ring 1 Mic, Ring 2 Ear, Ring 3 Ear, (Ring 1
next to tip) Mating Socket 626, NSN:5935-99-949-1940