Ampex 472 Studio (1985-1993 US)

Yes, your eyes did not deceive you. This is a C-05. i.e. 2.5 minutes of recording time per side, a type II premium tape from Ampex.
It is so rare, that the Ultimate Guide for Audio Cassettes Blank Tapes gave them a price point of $100!
We priced them more reasonably, despite them being literally "unobtanium". 

We did record a few of these and found them to be comparable to other premium type II tapes of the day such as the Maxell XLII and the TDK SA. Sweet highs, detailed midrange, low noise, and natural, unemphasized bass.

There is very little information on the Ampex branded 472 formulation, but after they spun off the Quantegy brand, we did find this overview on the same formulation:
"Quantegy 472 offers superior performance, unsurpassed reliability, and outstanding audio quality. Each component of 472 has been carefully designed to meet the exacting standards of the most discriminating cassette user.
Quantegy 472 cassettes utilize a precision five-screw cassette shell made of a high performance polycarbonate material. The high-impact resistance of the shell material makes Quantegy 472 cassettes less vulnerable to damage from rough handling. The tape used in our 472 cassettes is a special high bias formulation that meets the IEC Type II requirements for high performance cassette products."