The Remspec ATR head is held in place on the end of the probe shaft by a screw cap for close optical coupling. The overall probe diameter of 6 mm (approximately 1/4 inch) is maintained for good access to very small reactors. This particular head is fitted with a diamond crystal suitable for use in highly corrosive and chemically reactive environments, often in combination with a ruggedized shaft made of Hastelloy or titanium. It is a true diamond ATR element -- not a diamond-coated crystal -- and is nominally a "2-bounce" geometry.