The 19mm is correct, like gohounds said. 2 on the top and 2 on the bottom. 19mm or 3/4" wrench fit them.
The bolts themselves are 1/2X13 thread.
Yours have just been changed by a PO to a normal bolt instead of those POS torx heads.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...