These grinders are precisely constructed with completely interchangeable parts to allow easier cleaning or replacement of damaged mortars. They are designed for use in preparation of tissue homogenates and other similar applications. The PTFE pestle is for soft tissue such as brain or liver. The stainless steel rod is 0.25" (6.3mm) in diameter. The grinding chamber clearance is .004" to .006" (0.1 to 0.15mm). Manufactured from Wheaton 33 low extractable borosilicate glass that conforms to USP Type I and ASTM E-438 Type I, Class A requirements. Autoclavable.