These Carriage/Coach bolts seemed to be an almost perfect size for modification to fit my tee-slots.
They were also a whole lot cheaper than 'official' tee-slot bolts.
The tee-slot bolts described here have a much bigger flat support area, than the ones I bought from a supplier (this is one of the criticisms made of modified hexagonal bolts). The finished result seems to be fine for my purposes. Despite reading some negative comments about modifying the hexagonal heads of set screws and bolts, I set about producing my tee-slot bolts from some 'Carriage Bolts' (aka 'Coach Bolts') bought at my local 'pound' shop. It is surely relevant to any lathe, although the specifics given here are for my Myfold ML10. I needed some tee-slot bolts to fit my lathe.