hi....i like my sheaths to be made of one piece of leather, 3.5mm+, and by doing that when the holder part is folded round the end of it goes inside to form part of the welt....and its also extremely sturdy and being of thick leather it strays 'grippy' on the steel....if you use thinner leather....say 1.5mm (x2=3mm to equal the welt thickness) then i would think it prone to loosening....me personally, i would use the same leather as the sheath and, using a skiver, thin the two ends of the steel holder piece until theyre halved.....as dreadhead mentioned. as for belt loop....mix it up m8....i do it slightly different on each batch i make,....bit of uniqueness....do the stitching in a circle or a star, whatever!
have fun
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ps....i use artificial sinew and i triple-stitch the beltloop to the sheath body....its the one place you dont ever want the stitching to fail