mining rock bolts 1.diameter:16-25mm 2.used for in mines,tunnel 3.ISO,SGS,BV.professional factory 4. ... (grooved bolt)1.Diameter:16mm,18mm,20mm,22mm,25mm2.used for in mines,tunnel3.ISO,SGS,BV4. low price, good quality5 ... provide high bond strength in larger diameter borholes.2. Used for permanent support in mines and tunnels.3.with pin nut ...