Silo Bolts

For maximum strength of the joint, it is important to select the correct length of bolt. Longer bolts have a shank, and if the shank is too long, this will stop the nut tightening before the joint is fully closed, and the bolt will spin, damaging the glass coating; a bolt that is too short will not have enough thread for the nut to grip properly. In the joint, the shank of the bolt should be in shear, not the threaded part of the bolt. To work out the length of silo bolt required, measure the thickness of all the pieces that will make up the joint. Add these thicknesses together, and consult the chart below.

E.g. The vertical seam in the top ring of a silo: 2.0 mm sheet +2.0 mm sheet = 4.0mm.

From the chart below, a 1” bolt would be used here; or, the base angle to the bottom ring of sheets, at the corner joint between two sheets of a slurry store: 4 mm sheet+ 4 mm sheet + 6 mm angle = 14mm. Again, using the chart a 1½” bolt should be used here.

Total thickness of material
4.0 mm to 6.5 mm
7.0 mm to 10.5 mm
11.0 mm to 15 mm
16 mm lo 19 mm
20 mm to 23 mm

Length of holt required
1″ bolt grade 8.8
1¼” bolt grade 8.8
1½” bolt grade 10.9
1¾” bolt grade 10.9
2″ bolt grade 10.9