One of the first questions I had when I began to study the robot in earnest concerned the function of the strange hooks on the robot's wrists as well as the strange pegs in the arm bays. More experienced and knowledgeable robot builders quickly and politely answered my questions. They refered to me to excellent websites such as that created by master B9 builder Michael Davis, where the answers to many important questions can be found.

Bob May, the actor inside the robot costume during the run of  Lost in Space, used the pegs and wrist latches to lock the robot's arms in their retracted position. This enabled him to perform all manner of stunts, such as spinning the torso around 360 decrees.

The curvaceous wrist latches secured the retracted arms in the arm bays. They hooked around the pegs that protruded from the ceiling and floor of the arm bays. Each wrist had two latches, one in the 12 o'clock position,

and another in the 6 o'clock position:

The decision to place the screw that tightens the wrist clamp at the bottom of the arm rather than on the outer side was aesthetically correct, but functionally unfortunate. In early first-season episodes, it can be seen that the sharp screw assembly on the left arm had taken a substantial gouge out of the lower lip of the arm bay. Here is a screen grab from the first season episode "Island in the Sky" (episode 3, original air date: 29 September 1965), the beginnings of a gouge that would grow progressively more serious can be seen emerging in lower lip of the robot's left arm bay.

The latches hooked onto pegs that protruded from the ceiling and floor of the arm bay. You can easily see the lower peg projecting upward in the photograph above. In this next photograph, you can see both the upper peg and the corresponding upper latch:

 

Note how scuffed, scarred, chipped, and tattered the wrists are in this early publicity photograph! This is just a small glimpse into how much wear the robot costume took during the course of filming.

I have a set of resin wrist latches for each arm, but I am having them copied in steel. Although my robot will probably not be as energetically animated as the original costume with Bob May inside, the potential for latches of such a soft material to break is still too high for my taste. The problem for the machinist is that the latches curve over the wrist clamp. This will be difficult and expensive to create. This is a classic illustration of a proportional relationship I have discovered: In the realm of B9 robot building, there is an inverse relationship between cost and size: The smaller the part, the more expensive it is to create.