I have an HP Velotechnik Scorpion recumbent trike. The handlebars are upright and, since they have twist shifters, there is no place to mount accessories (horns, phones, gps, trackers, etc.) This T-bar accessory mount fits into the top handle bar tube and tightens via a securing bolt.
The 6mm x 110mm bolts used are for bunk beds, and the securing nut fits inside the tightening wedge. I printed both parts on an OPXL2H using input shaper and .32 structural. You need to print the handle upside down to minimize supports. I used supports on the bed side of the model to make it more secure. For the wedge use supports and a brim.
Bolts: https://www.amazon.com/dp/B07C61Q3P2
Simply place the securing nut inside the expanding wedge and then slide the assembly into the expanding fins on the handle. Thread the bolt down the handle and tighten slightly to secure the assembly. You can then slide the whole assembly into the handlebar tube and tighten securely.
The author marked this model as their own original creation.