This is a brand new master cylinder (not rebuilt like many cheap options) for upgrading the braking system of your E30. Have you fitted larger brakes? If so chances are the pedal is a bit softer now and this is a good way to remedy this and firm up your brake pedal. Also a good upgrade for more pedal feel even with standard brakes.
This is a direct fit to ABS equipped E30s, otherwise a small line and tee piece are needed (option available from dropdown).