SICK VL18-4N3212 Photoelectric retro-reflective sensor. SICK VL18-4N3212 is a archive in the V18 family. SICK identifies this exact configuration as manufacturer article 6013540. The official technical record specifies Functional principle: Photoelectric retro-reflective sensor; Dimensions (W x H x D): 18 mm x 18 mm x 63.6 mm; Housing design (light emission): Cylindrical; Housing length: 63.6 mm; Thread diameter (housing): M18 x 1; Optical axis: Axial. The linked SICK data sheet is specific to VL18-4N3212.