What are the really unusual or weird computers?

Yes they are half inch. What I meant was that they are not 'industry standard' half inch tape with large expanding hubs with the write protect ring in a groove in the reel. Instead the centres are much smaller, allowing 3200 feet on the same outside diameter spool as a 2400 foot reel using the same thickness tape (not the ultra thin tape). The reels are aluminium, not plastic, their centres have three notches which three matching 'fingers' within the hub fit into, holding the reel onto the hub. Some TM4s were fitted with small expanding hubs (the ones on the Leo and maybe others), but this did not fit 'industry standard' reels. The same design of hub is used on tapes of quarter inch, half inch, one inch, two inch and three inch, maybe other sizes too. I do not mean domestic quarter inch tape recorders, these use a simple nut on a stud. The write protect ring protrudes from the back of the reel, and three projections on the ring fit into three holes in the reel. The tapes themselves have a metalised leader which is electrically sensed by the deck. They also have a reflective early end of tape marker like later tapes, and I think they have a metalised leader at the end of tape, though I've never unreeled 3200 feet of tape to find out.