[sammyg2]

More info:

(dad's company) made the ablative insulating rings (kick rings) that covered the flanges of the solid booster segments. The solid booster was made in sections, appoximately 12' long by 18' in diameter. Solid propellent was cast and cured inside the steel cylinders and then machined to the final ballistic configuration.
These segments were shipped by rail from Thiokol in Utah to the Cape where thay were stacked with o-rings between the flanges.
After assembly of the motor segments, the "Kick Rings" were used to cover the flanges. The kick rings were ablative insulators designed to prevent the extreme heat from burning through the steel motor cases. The "kick rings" were fabricated by laying up silica-phenolic fabric patterns and then curing in an auotclave. The cured rings were then machined to the final configuration. Each ring was made up of several segments that were assembled into the final ring when installed on the booster motor.