1 Module Worm GearSome gears are blackened and shipped randomly.Material: 40cr quenched and tempered heat medication HRC25Speed ratio: 1:5/1:10Number of teeth: 20 Hole diameter: 6/8/10MM Worm difference: 2/4-threadworm 1: 20/30/40/50/60 Worm=single thread worm (in other links) 1: 10=Two threadworm 1: 5=Four- threadworm (If the malicious program gears are the same, the extra thread worms (1-4) there are, the lower the discount ratio of the 4-thread bug head compared to the double head, and it is also much less smooth to attain self-locking.)