Just seems to be made of steel mate. I didnt measure it, the guy who built the motor i used it from said it was desgined to drop the compression one point. Its about 1mm thick i think.

Why a decompression plate?

Here in South Africa we have a quality gasket manufacturer called Payon. I can get a custom made head gasket of max thickness of 3mm. With a decomp plate I would feel there is a extra place where it can blow through(between block and decomp plate,between decomp plate and gasket or between gasket and head).
With only head gasket it will be between block and head gasket or head gasket and head.

Just a thought. Curious what you guys think about a extra thicker head gasket.

Jeff thought a decomp plate was the way to go. Carbon buildup due to inefficient fuel burning is the reason to detonation.

This Plate was designed to drop compression one point for stock Aseries.