Is it some kind of spreader/sex toy?

used by electricians or telecom people?

It is not used by architects, electricians, or telecom people. I don't consider any of those professionals to be craftsmen (although draftsman rhymes with craftsman).

leather work, carpentry, glass blowing?

No, no, and no.

Is it a tensioner of some sort used by an upholsterer?

No. It is not used in furniture making.

Kyle, the reason I mentioned your dad had to do with Studio In The Country.

Studio In The Country: a sound studio? Therefore, is it a tool for stretching/tensioning a drum set, or a stringed instrument?