the rear dif is locked. Were can I get parts?
Ask someone with a lathe to make a sleeve out of brass. One side of the sleeve should have an internal diameter equal to the outside diameter of the copper tube; the other side of the sleeve will have an ID a tiny bit larger than the OD of the glass tube. Needless to say, there is a hole that goes right through the sleeve. Solder the sleeve onto the copper tube and glue it to the glass tube using an epoxy glue (provided the temperature will not exceed 100C; if it will get higher than 100C, use a ceramic cement). Be sure to do the soldering first otherwise the heat will crack the glass.
You don't need goggles for all laser light. For something at 20mW though you probably should especially if there is a chance that the beam might be reflected into your eyes (I'm assuming you don't plan on just looking at it directly). Laser Safety (yours would be class 3B):
