With it’s shaft in only one piece, the duplex system offers an economical solution to adjust and set backlash. Therefore worm gear can be almost backlash free.
The shaft worm’s has 2 different pitches, one for each flank. Thus the thread worm’s thickness is different at each ends.
Note that for the duplex system to work perfectly, the shaft must be adjusted with spacer.
When the shaft is pushed back the wheel is blocked.
For application where accuracy is not an option, such as worm gears for rotary table, we do recommend the OTT design