Tie bar to steering box bolts

Had a strange clicking noise on the steering and found the bolts securing the tie bar to the steering box were loose. Tried to torque them up again but the threads are damaged.

No big deal but I can't identify what size the bolts are and wondered if anybody could tell me what bolts and nylock nuts I need to buy so I can replce 'em. I know they are imperial with a fairly fine thread so probably a UNF.

Cheers.