The type of flexible brass tubing which is best for bulb horns and other places where air tightness is required is usually of the type known as “hot air” tubing. It differs from plain flexible tubing or conduit in that there is an asbestos or fabric gasket strip between the convolutions of the tubing which acts as a seal.

In cases where common flexible brass tubing is available, but the “hot air” type is not, the same effect can often be obtained by making the actual connections with rubber tubing placed inside the flexible brass tubing which then acts only to create the proper appearance.

Antique Automobile- 1946