Bosch Meat Grinder 4 Prong Blade 

This is the blade the comes with the meat grinder.  Replacement blade for the meat grinder (4 blades) When you purchase the Bosch Meat Grinder attachment for the Universal mixer, a four-bladed knife is included. Additional blades are available in either four-blade or two-blade configuration. The two-bladed knife makes larger chunks than the four-bladed knife.

If you grind much, it's best to have a knife for each disk because they'll develop a mated wear pattern over time and will cut best (rather than mushing) if you keep one knife paired with one blade. If you grind only occasionally, one knife will work fine for all disks, but you may want to carry a spare in case of loss or for eventual replacement due to wear.