Exhaust camshaft stud, why not a bolt?

[Jonnyfozz]

Can anyone with any technical or engineering wisdom explain to me why Renault have used a stud for the exhaust camshaft with different thread pitches on either side - (camshaft side m10x1.25mm pitch) (pulley nut side m10x1.0mm pitch) and the nut m10x1.0mm pitch obviously with 18mm spanner head and large thick flange. Whats stopping me from buying and fitting an m10x1.25mm pitch flanged Hex bolt 10.9 high tensile grade with whatever length matched the thickness of the pulley and enough thread into the camshaft? Ive seen that ktec sell a similar bolt which is advertised for use with Catcam aftermarket camshafts but after searching the forums it appears no one has suggested a bolt to replace the stud and nut before, maybe a good genuine reason why it was designed this way?

if anyone has any technical info on this drop it below as just curious