BS 4568 Class 4 gi conduit hot dip galvanized elrctrical conduit Specifications: Outside Diameter Length of Thread Pipe Size Min Max Wall Thicknessï¼?mmï¼? Length(m) Min Max 20 19.7mm 20mm 1.2-1.6 3.75 13mm 15mm 25 24.6mm 25mm 1.2-1.6 3.75 16mm 18mm 32 31.6mm 32mm 1.2-1.6 3.75 18mm 20mm 40 39.6mm 40mm 1.2-1.6 3.75 19mm 22mm 50 49.6mm 59mm 1.2-1.6 3.75 19mm 22mm