Based on the other holder arms provided by @BaGooN, I created a version to perfectly fit my TS100 soldering iron. This design uses only one screw for retaining the soldering iron, to preserve the ability to press both buttons on the side of the soldering iron. In my test print, I found one screw to be totally sufficient to hold the soldering iron rigidly. 

If you haven't yet purchased a heat insert adapter for your TS100/TS101, I discovered this link (I am not affiliated):

Material: PLA
Process: 3D Printed (FDM)

• High quality PLA print
• Made to order
• Carefully inspected before shipping

What's included: One (1) TS100/TS101 Soldering Iron Holder Arm for Heat Insert Press as pictured.

Approx. size: 31 x 107 x 41 mm · Est. weight: ~23 g PLA · Filament: ~7.8 m

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Design credit: "TS100/TS101 Soldering Iron Holder Arm for Heat Insert Press" by Ryan G, shared on Printables under the Creative Commons Attribution-ShareAlike 4.0 (CC-BY-SA 4.0) license — a remix of "Heat Insert Press" by Unknown. Printed as designed; no modifications to the original.