To ensure safety without removing burrs by an after-processing step.

A light proofing part 20 composed of a half-transparent black colored resin obtained by incorporating carbon black into the first synthetic resin material consisting of a light proof resin material is formed from a central part to an inner part at an upper site of an apprentice 3 including a collar body 2, and a light transmitting part 21 and a spreading part 21a, which are composed of the second synthetic resin material consisting of a light transmitting resin material, are formed at a bottom side and an upper side setting from a bottom side in such a way as covering the light proofing part 20 from an outer side. A protection part 37 structured by an expressing surface 33 of a burr 31 formed along a burr 31 and a wall surface 35 equipped in the expressing surface 33 at a height higher than the expressing surface of a burr 31 is formed at the light transmitting part 21 and at the light proofing part 20 in both sides of a boundary part 23.

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