I´m not completely sure. My source (Ground Power Special Issue February 2008 "Less known army ordnance of the rising sun pt. 2") only gives "37 mm Flak Rheinmetall" for both versions.
As far as I´m able to interprete the pictures and captions the ST24 was the 3,7 cm ST 10-100 and the ST22 was the Flak 18.
IJA tested the 37 mm Flak 18 barrel with a triangular lafette, too. But the final type 1 37 mm aa-gun had the cruciform lafette.
Yours
tom!
P.S.
I wrote the caption of my 37 mm gun picture before I realised that it was the ST 10-100 version (I thought of a Flak 36 test...
).
