Righetti Steering columns are an aftermarket option for many chassis brands.
The OTK / Tonykart model is M10 x 500mm which uses a 10mm stud meant for a 10mm bearing at the lower support (common on old style OTK)
The Birel and CRG options are M8x510mm and use a 8mm stud meant for a 8mm bearing at the lower support
The CRG cadet measures M8x420mm and use a 8mm stud meant for a 8mm bearing at the lower support
The XXS baby kart has a single tie rod mounting bracket and measures M8x390 and uses a 8mm stud meant for a 8mm bearing at the lower support