Gunpla HG action base adapter with 3 mm peg
A small saddle that lets High Grade Gunpla kits without a dedicated stand hole sit on a Bandai Action Base 4 or 5 arm. The arm ends in a 3 mm peg, so the adapter has a 3.1 mm socket 8 mm deep underneath and a curved 28 mm wide cradle on top that hugs the kit's crotch block between the hip joints, with 1 mm soft lips that grip the skirt armour rather than scratching it. A 5 mm hole through the side takes an optional M3 grub screw for heavier kits. Print it upright with 2 mm walls at 0.12 mm layers so the peg socket is round.
Every kit's waist is a slightly different width, which is why one adapter never fits all. Describe the crotch block of your Gundam in SpeakCAD, preview the adapter in the browser without charge, ask for a wider cradle for a Zaku or a 5 mm peg for MG kits in the chat, and download the STL.
Model a Gunpla action base adapter 30 x 20 x 18 mm with a 3.1 mm socket 8 mm deep underneath for a Bandai Action Base 5 peg, a curved 28 mm wide cradle on top with 1 mm retaining lips for an HG crotch block, a 2.5 mm side hole for an M3 grub screw and 2 mm walls.