A link unit comprising: two spaced-apart outer chain plates, each of said outer chain plates having a first end section, a second end section that is spaced apart from said first end section, an inner side surface that faces the other one of said outer chain plates, and an outer side surface that is opposite to said inner side surface, said first end section of each of said outer chain plates having a through hole, said second end section of each of said outer chain plates having a connecting hole that has a first hole portion, a second hole portion, and a neck portion located between said first and second hole portions (201, 202); two spaced-apart inner chain plates, each of said inner chain plates having a first end section, and a second end section that is spaced apart from said first end section of said inner chain plate, said second end sections of said inner chain plates being disposed between said first end sections of said outer chain plates; a connecting pin being inserted through said second end sections of said inner chain plates and said first end sections of said outer chain plates; an assembling pin inserted removably through said connecting hole of each of said outer chain plates, said assembling pin has a main pin body, two neck sections each of which is connected to a respective one of two opposite longitudinal ends of said main pin body, and two end sections each of which is connected to an end of a respective one of said neck sections distal from said main pin body said first hole portion of said connecting hole of each of said outer chain plates having a diameter greater than that of said main pin body and at least one of said end sections of said assembling pin, characterized in that each of said neck sections has a diameter greater than the width of said neck portion of said connecting hole of each of said outer chain plates, said first end section of each of said inner chain plates has a first annular flange that extends toward said first end section of the other one of said inner chain plates and said second end section of each of said inner chain plates has a second annular flange that extends toward said second end section of the other one of said inner chain plates. two spaced-apart outer chain plates, each of said outer chain plates having a first end section, a second end section that is spaced apart from said first end section, an inner side surface that faces the other one of said outer chain plates, and an outer side surface that is opposite to said inner side surface, said first end section of each of said outer chain plates having a through hole, said second end section of each of said outer chain plates having a connecting hole that has a first hole portion, a second hole portion, and a neck portion located between said first and second hole portions (201, 202); two spaced-apart inner chain plates, each of said inner chain plates having a first end section, and a second end section that is spaced apart from said first end section of said inner chain plate, said second end sections of said inner chain plates being disposed between said first end sections of said outer chain plates; a connecting pin being inserted through said second end sections of said inner chain plates and said first end sections of said outer chain plates; an assembling pin inserted removably through said connecting hole of each of said outer chain plates, said assembling pin has a main pin body, two neck sections each of which is connected to a respective one of two opposite longitudinal ends of said main pin body, and two end sections each of which is connected to an end of a respective one of said neck sections distal from said main pin body said first hole portion of said connecting hole of each of said outer chain plates having a diameter greater than that of said main pin body and at least one of said end sections of said assembling pin, characterized in that each of said neck sections has a diameter greater than the width of said neck portion of said connecting hole of each of said outer chain plates, said first end section of each of said inner chain plates has a first annular flange that extends toward said first end section of the other one of said inner chain plates and said second end section of each of said inner chain plates has a second annular flange that extends toward said second end section of the other one of said inner chain plates. characterized in that each of said neck sections has a diameter greater than the width of said neck portion of said connecting hole of each of said outer chain plates, said first end section of each of said inner chain plates has a first annular flange that extends toward said first end section of the other one of said inner chain plates and said second end section of each of said inner chain plates has a second annular flange that extends toward said second end section of the other one of said inner chain plates.