I've just acquired a pristine set of Asahi Pentax Macro tubes ( ) and the seller also had this......... (and I had a GAS attack)
SIGMA TELE-MACRO MULTI-COATED 2X - 1:1
Even though it appears to be in unused condition I suspect it is probably about 30 years old. Google tells me it was made in all the popular mounts.
Interestingly the glass elements are designed to be easily removed, simply by unscrewing them, giving you about a 42mm macro tube with aperture lug.
I suspect that this little gem (?) was made for one or more specific Sigma telephoto models.
Anyone familiar with it ?