Join Date: Mar 2012
Yes, kabutowari and hachiwari are synonyms. Both are old names. To complicate matters, it seems there were individual swords named "hachiwari", and kabutowari (or hachiwari) is also the usual term for testing swords by attempting to cut helmets with them.
Of these pictured examples, the 1st (as mentioned above, this is a tekkan) and the last are not kabutowari. Kabutowari need the hook and the curved "blade". The hook is on the inside of the curve (which is the front, according to most depictions of use I've seen).
The last weapon is a jutte. Sword-hilted jutte are unusual, but known. (Perhaps some writers classify them as kabutowari/hachiwari on the basis of the mountings?)
The first weapon is also called tetto as well as tekkan (both meaning "iron sword"). Don Cunningham (Samurai Weapons) calls weapon #3 (i.e., photo 4) a "tekkan made in the shape of hachiwari or kabutowari" (also saying the same about a tetto like weapon #1).
At hand are a supposedly-old tetto like #1, weighing 380g, and a modern kabutowari, with 14" "blade" and of quite stout construction, weighing 580g. Both are far too short and light for serious use as suburito, and will be poor against armour. (I think my kabutowari is the one sold by Bugei; their advertising blurb says "It could be used to break helmets and other armor" but I thoroughly doubt this.)