KM-15A oxygen appears to be a predecessor of KM-15I oxygen mask. Same simple small rubber body, but this time it has two small opening on the lower side of the body - these are used to get exhaled air out of the mask. Air is delivered into the mask via thin rubber hose - there is no inhale valve thus KM-15A is a constant oxygen flow oxygen mask. Inside edges of the mask are lined with leather to make mask more comfortable to wear.

Unlike KM-15I which is kept on pilot's head with a simple rubber strap, KM-15A oxygen mask uses elastic material strap system. Strap system is made out of 5 different straps - two small main straps connected each to one side of the mask. Horizontal strap attached on the ends of both main straps and adjust how tight mask should sit on pilot's face. Vertical strap is also attached on both ends to main straps and is used to prevent mask from sliding down on pilot's face. Finally there is a strap that connect vertical and horizontal straps on the back - it is used to control position of the vertical strap thus preveting mask from sliding up or down.

 

Front view of KM-15A oxygen mask.
Right side of the mask. Not small main strap connected to horizontal and vertical straps.
Left view of the mask.
This picture shows how strap system is arranged on the back. Small strap strap that connects vertical and horizontal strap control position of the mask on the head preventing it from either sliding up or down.
Located on the left side of the mask is a stamp that shows mask's designation.
On the front side of the mask, just above the place where oxygen hose connects to the mask's body is a stamp with several circles of different diameters.
Located just underneath the oxygen hose are two small holes used to allow excess air to escape out of the oxygen mask.
View inside of the mask. Note that edges are covered with leather to allow for more comfortable wear.
Close up on a stamp located inside of the mask's body. Bottom part of the mask in up.