the inside copper ring are bent(not round all around) and the plastic cap was pushed in the hole improperly before shipping(which caused a bent on a copper ring). Consequently, my eyepieces can't fit. I'll have to disassemble and repair. Quality control is the problem. Also, the groove for the copper ring isn't eccentric or the copper ring isn't thick enough to do it's job, so when you tight the side screw, the eyepiece is pushed to the opposite side instead of being clamp in the middle by the copper ring. the focuser mechanism work great and is very smooth. The quality of the material are good. I recommend it for DIY project.
Sturdy construction and smooth movement. This should be fine for my Dobson under construction.