FILL PLUG FOR HYDRAULIC DEVICE

摘要

High-performance sealing of a through hole in which pressure is high can be realized by tightening a filler plug with respect to an internal thread portion formed in an oil passage of a hydraulic device at a high tightening torque. In addition, the hydraulic device can be reduced in size and cost by realizing a small height of a head portion of the filler plug. The filler plug is configured such that: a head portion (16) is formed on an upper end portion of an external thread portion (15); a sealing portion (18) formed at the head portion (16) can be caused to strongly contact a funnel-shaped inclined inner peripheral surface (19) formed at one end of an internal thread portion (14) formed in an oil passage (13) of the hydraulic device (12) by tightening the external thread portion (15) with respect to the internal thread portion (14); an upper peripheral surface portion of the sealing portion (18) is formed as a tapered portion (22); a circular constricted portion (21) is formed between the sealing portion (18) and the upper end portion of the external thread portion (15); and a dimensionless value of a head portion height H1 from an upper end surface of the head portion (16) to the sealing portion (18), that is, a dimensionless value obtained by dividing the head portion height H1 by a nominal designation value of the external thread portion (15) ranges from 0.4 to 0.7.