The "three links" of trade, mail, and air and shipping services between mainland China and Taiwan; specifically 通商tōngshāng, 通邮tōngyóu, and 通航tōngháng
T-joint
A pipe fitting or plug with three connection ports, such as a tee joint or three-way plug
three connections
The three basic utilities that must be provided to a construction site: water, electricity, and road access