Panasonic square head fibers provide a combination of break-free (10 million times bending durability [typical value, when bent back and forth at 180° with a bending radius of R10 mm R0.394 in]) and bendable (bending radius of R2 to R4 mm R0.079 to R0.157 in) characteristics. The fiber ber core will not harden or break, even in environments where oil is present. The head, nut, and washer are made from rust-resistant SUS304. The unbreakable tough fiber with high durability is covered in a fluorine resin tube. The fiber head is also covered with a fluorine resin component, achieving a high level of environmental resistance. Fibers deliver stable detection, since the sensing part is sealed with fluorine resin, which does not allow oil penetration. Additionally, the detection part features a convex design made of fluorine resin, achieving lower friction than glass.