ALVIS STALWART, SARACEN, SALADIN -  Pipe Diameter 3/8" HYDRAULIC TUBE NUT (Hydraulic Pipe Connection Nut) X2

NSN: 2530-99-800-3794 / P/N: AULK/31385

The thread is 5/8" UNF (18 TPI) with internal taper for pipe flared end. 

Buy it now for 2 Nuts, multiple available (postage discounted for multiple purchases) 

Parts manual references, as pictured:

STALWART G25, QTY As Req

STALWART G37 QTY As Req

STALWART H14, QTY 1 Used

The last picture shows the connection to the Accumulator to show the fitment.