This is a trolley for standard 1-5/8"x1-5/8" strut channel. There are versions for 6001 and 608 bearings- 28x12x8 and 22x8x7mm (ODxIDxW), respectively. They both have a 12mm hole through them to hang either a threaded eyelet or hook from.

As pictured, they have heavy duty bicycle wheel hooks- good for 70 pounds, but not yet load tested (see the end of this section for a load test update). The hooks are from Home Depot- Husky 7/16 in x 8-1/2 in Black Bike Hangers. They have a wood thread that I partially filed a few threads down on and threaded with a die for a 3/8" machine screw. The nut secures pretty well at the end of the threads, but for better security/retention you can use thread locker, a locknut, or jam nut, though you may need to change the NutThickness parameter in the Fusion 360 model file to make more room for the latter 2 items.

The 6001 version is also pictured with a 21x12x5mm (ODxIDxThickness) thrust bearing so the hook can spin easily and not wear at the trolley. This is probably overkill and a simple flat washer could be used instead.

Edit: After making a few variations, the thrust bearing is definitely overkill- a bit of friction is nice so the hook stays in position instead of drifting to wherever the center of mass is lowest because things are tilted slightly. This also goes for the bearings: these trolleys can roll down a 0.5° slope, so this would be a good use of rough, crunchy bearings unless you want to find the lowest part of your track. I also prefer using the 608 bearings under the assumption that the smaller bearings have a bit more drag or catch more easily on any imperfections on the strut.

The Fusion 360 model file also has provision for a spring to push up on the thrust washer to help hold the trolley in place when it has no weight hanging from it, but I have not tried that yet the spring I used is good for a bit of friction- it will not really lock the trolley and hook into place. Most dimensions are parameterized (bearing, nut, thrust washer, spring, and trolley dimensions) and can be changed. As I usually do, there is also a parameter- KludgeOversize- to compensate for my printer making holes smaller than specified. This may not be necessary if you already make this compensation in your slicer, such as Horizontal Expansion in Cura. The outer dimensions were close enough that I just needed to trim a bit where the 3D print sagged at the bottoms of the axles, otherwise the bearings pressed on relatively easily, but seemingly tight enough that they won't slip off.

Some of the STL files have the parts upside down. After flipping them, print them with supports on the build plate only, relatively many walls and high infill. I printed at 50-60% cubic infill, but I'll repeat: I have not load tested these besides hanging a bit much of my body weight from them. These parts were printed with PETG, but you could probably use other materials. I am not up to date enough on filament materials to make any recommendations.

This has barely been optimized for Unistrut P1000 12 gauge strut channel. The parts should work on 14 gauge too, but the WheelToWheelWidth might need to be increased a little.

I built the pictured eyebolt version (with 608 bearings, a 16mm spring, flat washer and 2 jam nuts) with 8 layer walls, 60% cubic infill PETG. It held most of my 150+ pounds of weight. I do not have any measurement tools to load test it to destruction.