Thanks to everyone for the awesome help.
nice resistors, but probably adictive - so send them to me. ;-)))
Would like to know the manufacturer.
I have quite a bunch of those resistors. Some have odd values (817Ohm, 1.91kOhm) and some surprisingly low tolerances. The best one is 10kOhm 0.001%). Here is a picture of the entire set. For reference I added a ruler and a 7W power resistor. I'm not sure about the vendor all have that trinagle with an Ohm symbol inside maybe that is the manufacturer logo? I'm also not sure what "Rdm" stands for.
I found a post in a german forum where somone posted pictures of similar resistors. Someone there stated that those were "high temperature, low drift resistors for radar".