Shirley the thickness of the lead in a PP is defined by the size of the hole through which it's propelled. If you mean hardness, then I note that many carpenters' pencils are 2H.
There are several styles, here is a 2 mm one where you use an external sharpener to create a point
formatting link
I quite like the Pentel 0.9 mm which I use with 2B leads for marking up draft reports and writing on engineering drawings, this is OK for "delicate" woodwork but not suitable for studwork, etc.
I have a clutch pencil (rather than "propelling") with approx 2mm lead that withstands vigorous use quite well (and has a sharpener in the other end). Not sure how well it would work on rough sawn timber, but for that I might strike a line with a knife to make it easier for the pencil.
I haven't seen one of them for years - most mechanical pencils are the kind where pressing the end advances the (thin) lead by a fixed amount.
Presumably the OP is using the term "propelling pencil" in a loose way to refer to any kind of mechanical pencil. True propelling pencils you screw to end to advance the lead - usually the lead is loose as there is no clutch.
I think mine are 0.5mm (and about HB - they're mostly hotel freebies), but it depends on the surface and the accuracy you want. For marking on planed hardwood or plaster then 0.5mm seems OK, for sawn timber you probably want something a little bigger, and maybe softer. If you go larger than 1mm then either accuracy will be a little, errr, inaccurate or you'll need to sharpen.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.