hey there @Judi - welcome to the forum. I am not sure, but hopefully someone here can help.
Looks like a standard front loaded twist mechanism.
Just load one lead into the tip.
The chrome tip should first be screwed off. Then insert the brass helix with the front threads sticking out of the black part. Screw the tip back on to lock them together.
I have one of these old pencils (actually in a nice Staedtler set) that has what I always thought to be a blank metal lead… to make blank lines with a ruler for writing??
Was this even a thing?
That ‘blank’ is probably the ‘flat end’ of the propelling driver. It held on to the ends of lead cores by friction. Plenty of wiggle room for 0.9 or wider diameter cores.
Hmm, that could be it! I think what lead me to imagine a blank point was that as far as I remember it doesn’t recoil that far back into the pencil on order to house a lead… but it was a while ago, will check it again tonight
Thx!
The milled brass colored part is a friction fitting that is supposed to ‘lock’ into the opening in the tapered black piece. If it fits without falling out, hold the black piece in place and turn the shiny cone anti-clockwise until a small flat tip pokes out of the cone. This also ‘expels’ any remainder lead inside the mechanism.
Now turn the cone clockwise to retract the flat bit all the way back inside as far as it would go. Then insert a piece of lead from the front.
Turn the cone anti-clockwise slightly to extend the lead by 2-3mm. Point the lead down on a table surface and nudge the lead firmly into the back of the pencil, so that it is seated into the ‘flat bit’ inside. Now you can use the pencil without fearing that the lead might slip out by itself.
Note: some brands turn the cone, while others fix the cone and have you turn the pen body itself. But the principle is the same.
You guys are right, the brass rod does seem to recoil enough to let a short lead in from the tip
PS. If anyone collects these and is interested drop me a line, I’m willing to sell this set for a fair price. Still not shipping to the US… I mean, there’s fresh news about this but I haven’t wrapped my head around the process yet.
@Judi Sorry for hi-jacking your thread 
Welcome and, please, carry on!