Facom Angled Open-Socket Wrench (75 series) - deep recess at one end and open end socket at the other fit over protruding studs (6-point, both ends). The angle and through hole design accommodates threaded rods or a bar for extra leverage without affecting wrench strength. This is one of my favorite Facom products for field installations (cabinets, shelving, garage door track, etc).
Note - I used this 7mm size for bleeding BMW brake calipers...6pt grip safely loosens stubborn bleeder nipples without rounding the edges.