The Belt Anti Skip set (BAS) is designed for Modified racing purpose with "big horsepower" and/or high traction conditions. 
It will support the rear belt with an additional ballbearing and prevents 100% from Belt skipping in every possible scenario. 

Info: 
This part/set fits only with AM177 Motormount. 

contains: 

1x AM111

1x B73SS 

1x SB3x5

1x SB25x6