I found this T-handle and liked the basic idea. However, looking at the files I recognized that the tip of the thread of the screw was screwed up in design (pun intended). Pretty simple, I corrected it in tinkercad. Then it dawned on me that a screw with a 4mm hole would be beneficial and followed a request and also made two even larger versions. The file names indicate the hole size, not the max size of the hex key! The 11-5mm is suited for up to 10mm.
After using them for a while I found that some keys really aren't perpendicular in the handle which is caused by then bend in the key. Simply chamfered the hole as much as possible and voilà, now it works better.
If you want it even larger, i.e. for a 1/2" key just take the 11-5 files (handle and screw!) and enlarge them in the slicer in X and Y to 127.5%.
The 7-3 screw fits into the 9-2 handle and the 4 and 6-3 in the small one (flipped).
Printed with 0.2mm adaptive layers and 20% cubic infill with double lines. No support.
The author hasn't provided the model origin yet.