I have a project that had specified a sign lighter type fluorescent to wash the face of the upper half of a tilt wall bldg. Problem is, it is to be mounted on 4" steel tubing. In my proposal, I told them they would have to cut 176 opening for me to get the locknut on the knuckle nipple. They asked for an alternate. I (& the manuf. rep) have been unsuccessful .. am about to give the problem back, but thought I would check with you guys first. Low profile, no surface mounted pancake boxes or conduit - all fished through the steel channel.