Acrylic salt and pepper grinders ... very dicey. They crack like bejingo if you tighten them too much. Make sure you put a blob of cooking oil on the screw at the top to keep them nice and lubricated and turn the grinder upside down before you tighten the nut to keep peppercorns out of the grinding wheels.
"You're a big man, but you're in bad shape. With me, it's a full time job." – Lt. Bromhead to Prince Dabulamanzi before the Battle of Rorke's Drift.