Patent ID: 8540597

Claim:
A connection unit of a chain, comprising: two outer link plates each having a first hole and a second hole, the second hole having a first recess and a second recess which communicates with the first recess, the first recess having a diameter larger a diameter of the second recess, the second recess including: an inner surface and a stepped engaging surface which is perpendicular to the inner surface; a stop surface perpendicularly extending from the engaging surface; and a combined conjunction surface formed at an intersection of a contact line of each of said first and second recesses, said combined conjunction surface forming a first conjunction surface extending from said contact line of said first recess to a second conjunction surface inclined with respect to said first conjunction surface and extending to a first protrusion, said first protrusion extending from the inner surface; a pin fixed in the first hole and including an engaging portion; and a neck located beside the engaging portion and having a diameter smaller than a diameter of the engaging portion.