Turn and Bank Indicator (Face only), Type A-1 Pre-WWII
This is the face section of the first Turn and Bank Indicator used in Pre-WWII aircraft of the Air Corps US Army: Type A-1. By the time WWII began, the common turn and bank indicator type was up to A-5. The serial number prefix is 27, and, if the serial numbering methodology is the same as used in WWII instruments, may have been manufactured in 1927.
The glass tube in intact and still contains fluid and the floating ball. Measures ~2.75 inches diameter and ~1 inch deep. Makes a nice little display item.