cap gasket

Colloquialism for "Cap Light Shield" an important part of an Altman 360Q ERS to prevent light leaks from the rear of the fixture.


http://www.productionadvantageonline.com/image/PA/5763.jpg
Altman part#20-0138, #360Q Cap Light Shield, USD 4.25.
AKA "blast shield," according to http://www.productionadvantageonline.com/Instrument-Parts/20-0138.aspx .

The Altman 360 takes a similar unit, but with slightly different cut-outs.