New master cylinder question

[74bronk]

See pics. What is this black boot that came with master cylinder? Use it or no use it? What is it?

Thanks

 

[EPB72]

looks like a universal type master cylinder.. If you have a vaccum booster or hyroboost you don't use the boot ,, If your running manual non assisted brakes you use the boot ,,, If you have assisted brakes you have to pay attention to the bore depth of the MC piston and what ever booster you have output pushrod