First, to make it a little easier, let's call hochiku hochiku and shakuhachi shakuhachi so that everyone knows what is what. The plural of "hochiku" is "hochiku" and the plural of "shakuhachi" is "shakuhachi"!
Hochiku, or as some write, Hocchiku, flutes are always (except for the exceptions) one piece flutes, without the familiar connecting joint near the center of the length. Shakuhachi are almost always made in two pieces with the joint near the center of the length. Any shakuhachi made in one piece is called "nobe". The "be" of "nobe" sounds like the "ba" of "baby". "Nobe" can be translated into English as "total".
Hochiku are usually much thicker (fatter) and longer than shakuhachi so are commonly heavier than shakuhachi.
More often than not hochiku have no inlay material (buffalo horn, ivory, plastic, whatever) at the mouthpiece. NOTE: "mouthpiece" is being changed to "utaguchi". The plural of "utaguchi" is "utaguchi".
The angle of the utaguchi plane of hochiku is closer to perpendicular to the length of the bamboo than utaguchi angles commonly seen on shakuhachi.
The size of the hole at the top of hochiku varies widely and can be quite large while the size of the hole at the top of shakuhachi is very nearly the same for all shakuhachi regardless of the length. The hole at the utaguchi end of shakuhachi varies a bit among shakuhachi makers but nowadays there is some consensus that things are generally easier when these open ends are all nearly the same in internal size. The external size varies widely, of course, depending on the fatness of the bamboo. What this means is that for shakuhachi with large bores there will be a thin wall partially closing the open end at the very top of the flute in the area where the shakuhachi is placed against one's chin. This little wall is called "iki kaeshi". "Iki" means breath and "kaeshi" means return. On some shakuhachi, and even hochiku, a thin ring of bamboo is inserted into the utaguchi end to replace part of the removed membrane and is then filed out in the area where the breath is blown over the edge, leaving a sort of crescent shaped partial ring of different color and texture. Sometimes material other than bamboo is used to reduce the size of the opening at the utaguchi, car body putty, resin, whatever.
Hochiku are mostly bamboo bores that have grown while shakuhachi are bamboo and some other material bores that have been made. 0n certain occasions for whatever reasons filling material is added to the grown bore while on other occasions for perhaps other reasons bamboo material is removed from the grown bore.
The membranes at the nodes of hochiku (on the inside) are removed to a lesser degree than the membranes at the nodes of shakuhachi.
The node membranes of hochiku are usually visible while the node membranes of shakuhachi are almost never visible.
The frequency of the lowest normal note (neither meru nor karu), Ro, of hochiku is not adjusted to any specified frequency. The frequency of the lowest normal note of shakuhachi is, these days, nearly always adjusted so some specified frequency of the equal temperament scale.
The frequencies of the fingering positions for all notes, other than Ro, of the open hole hochiku scale (Tsu, Re, Chi, Ri, Japanese Inakabushi Yosenpo) are not adjusted to conform precisely to any musical scale, nor are they adjusted to sound a specified musical distance from the basic tone (Ro). These same notes of the shakuhachi are almost always adjusted to conform to the the musical scale currently in vogue, nowadays, the equal temperament scale with A4 somewhere between 440 and 445 hz, depending upon with whom one is talking.
Finger hole location determination is about the the same for both hochiku and shakuhachi, being in most cases a sort of good guess full of hope.
Hochiku, as bamboo flutes and as a term used and understood by Kodama, are as long as or longer than about nishaku-gosun or rokusun. Some of the shorter big fat flutes used by Watazumi would not be hochiku according to Kodama. Further, what might be called semi-hochiku which have some but not a lot of filler in the bore (some call them "ji-nashi" = without "ji" or filler), could not be classes as hochiku by Kodama because of the added filler.
Bei Shu Shakuhachi Workshop