For context, this is a (rather old) Cullmann 2502. The head features a slot (30 x 5 mm) with two set screws on the front facing side (see other pictures). I thought it could be a mounting point for accessories but could not find any info online...
Front face with set screws:

Full tripod:


3 Comments
lemmefixdat4u@lemmy.world · 4 pts · 1y
Could the slot fit this accessory?
https://www.ebay.com/itm/326364663907
vk6flab@lemmy.radio · 3 pts · 1y
I'm giving you a wild guess, but I suspect it's to mount an arm to hold a flash, alternatively it's for a handle so the head can be rotated smoothly with a video camera mounted.
vk6flab@lemmy.radio · 1 pts · 1y
This looks like a contender:
https://www.ebay.co.uk/itm/113708069278