What does triple overflow mean? However, there are many existing dies (outer diameters) for PC round pipes and acrylic round pipes. The sizes of acrylic pipes are as follows: φ 6.5, φ 8.4, φ 1 11.9 (φ12) and φ/. φ 19、φ20、φ20.5、φ2 1.2、φ22.2、φ22.5、φ23、φ25、φ26、φ26.4、φ27、φ28、φ28.3、φ28.8、φ29.6、φ29.7、φ30、