Brass coupling , It can connect the motor and shaft or connect the diameter of the shaft.
It can satisfy the using demand of the general accuracy, So we can use it to make model aircraft,robot and so on.
Cross sectional diameter on both ends is 8.7mm, Cross sectional diameter in the middle is 7.3mm, The total length is 20mm.
2mm turn 3mm（Said the diameter of the hole is 2mm at one end, the other end is 3mm, So we can use it to connect the shaft of 2mm diameter with the shaft of 3mm diameter）
2mm turn 3mm,
3mm turn 5mm 3mm turn 4mm,
3.175mm turn 2mm,
3.175mm turn 3mm,
3.175mm turn 5mm,
3.175mm turn 3.175mm