We can't say for certain, but we theorize that, to save money on an already expensive Commodore PET computing system, designers skipped utilizing a standard IEEE-4888 on the back of the machine for disk drive attachment.  Instead, they used a money saving 12/24 .156" edge connector, which required no connector costs (it was just the edge of the motherboard PCB, etched into a set of connector "fingers").  At the time, it was an ingenius move.  Not only did they save money on the manufacture of the unit, but the connector was used no where else, so Commodore was essentially the only place to buy the required cabling (a mashup unit with a female edge connector on one end and a standard passthrough IEEE 488 Centronics(tm) 24 connector on the other). Needless to say, those cables were expensive then, and they are even more so today.

We considered designing and manufacturing a set, and then we regained our sanity.  PET owners need only 1 cbale per machine, and there are not enough owners today to make the minimums needed for custom manufacturing.  However, someone suggested we skip the "cable" part and just design a passive converter with the required connectors, a much more reasonable approach.

Thus, behold the fruits of that labor.  It's not incredibly cheap, we know, for the IEEE connector is still an expensive item, but it's far cheaper than buying the rare cable. There's little to fail on this device, as it has absolutely no active parts.  PCB, two connectors, wiring, we're done here.

Note: On the next product run, assuming there's 100 folks out there willing to grab this batch, we'll write "TOP" on the lettered part of the PCB, as it's a bit nonintuitive.  The IEEE connector should be "under" the PCB when installed (the PCB lettering should be "up").  There's a "key" indent in the IEEE 488 edge connector we'll try to leverage if we can find edge connector "keys" to install in these adapters.