FC-135 Tuning Fork Crystals Epson Timing FC-135 Tuning Fork Crystals are 32.768kHz (32kHz to 100kHz) frequency range crystals designed for small communications devices. Epson Timing FC-135 Tuning Fork Crystals feature 3.2mm x 1.5mm x 0.8mm external dimensions, a fundamental overtone order, and a 0.5µW (1µW maximum) level of drive. The series operates over a -40°C to +85°C operating temperature range.