You can use the following slot numbers in your blacklist.yml file:

Hotbar:               0 (left)  - 8  (right)
Upper inventory row:  9 (left)  - 17 (right)
Middle inventory row: 18 (left) - 26 (right)
Lower inventory row:  27 (left) - 35 (right)
Boots:                36
Leggings:             37
Chestplate:           38
Helmet:               39
Offhand:              40

Check out "slot-numbers.png" for a screenshot with all slot numbers.