This extension allows greater fluid volume without requiring a large-diameter reservoir. The taller column of fluid is also less likely to introduce air into the system under extreme cornering and braking. Fits the girling integral master cylinder with 1 3/4" threads. Translucent construction makes it easy to check the fluid level. The threaded base ring is metal to engage the threads on the Girling cylinder. Measures 2 1/4" from the top of the Girling reservoir to the top of the cap on the extension.