Found Rubber eyecup for Soligor Spot Sensor II spotmeter

I recently got a Soligor Spot Sensor II spotmeter, & it doesnt have the eyecup for it.
Looking for a generic eyecup for it, so if anybody knows what size would fit on it (or something close to it), thanks!

Uploaded a pic of the eyecup thats shown in the manual, it doesnt have to be the exact same one.

Get some measurements and search for telescope binocular eyepiece rubber cup?