A mine crib from interlocking planks has pair of jack planks on opposite slides of the crib comprising an upper plank 19, lower plank 20 equipped with plates 23 and 24 having screw holes 34, 35 and threaded rod pass through holes 36, 37 and 38 so that threaded rods 39, 40 and 41 may slide through the holes and passing to corresponding cavities 42, 43 and 44 in plank 19. Each rod has a nut 45 and washer 46 so that the nut may be used with an appropriate tool so that as the nuts wound upward along the threaded rods then the jack plank sections 19 and 20 may be jacked apart and be used to preload the crib.