... SGS,BV.professional factory 4.low price, good quality mining rock bolts(grooved bolt)1.Diameter:16mm,18mm,20mm ... bolt includes 3½ paddle configuration to mprove resin mixing and consequetly provide high bond strength in larger diameter borholes. ... 2. Used for permanent support in mines and tunnels.3.with pin nut device, nut could ... square. thickness, 4mm,5mm,6mm,8mm,10mm, and so on.