This is a very nice 4" cone midrange, which is featured in the HUMAN 88-41.
It features a carefully designed polymer cone, with a butyl rubber surround.
The outside mounting (rabbet) diameter is 4.-1/2", with a cut depth of 1/8". The through-hole should be 3-3/4".
For a functional Q of about 0.7, it should be in a 2 liter subenclosure, which is about 4 x 4 x 8".