SICK GRL18SG-F233Z Photoelectric sensors. SICK GRL18SG-F233Z is a photoelectric sensors in the GR18 family. SICK identifies this exact configuration as manufacturer article 1059556. The official technical record specifies Functional principle: Photoelectric retro-reflective sensor; Functional principle detail: With minimum distance to reflector (dual lens system); Dimensions (W x H x D): 18 mm x 18 mm x 38.1 mm; Housing design (light emission): Cylindrical; Thread diameter (housing): M18 x 1; Optical axis: Axial, fully flush. The linked SICK data sheet is specific to GRL18SG-F233Z.