Thunderbolt is a 8.8 grade self tapping anchor for use in concrete, brick, stone & block. The Thunderbolt can be used in both solid & hollow materials. Thunderbolt is now the fastest selling anchor bolt on the market. Please be aware: If you are comparing prices with our competitors please make sure that you comparing the correct size. You will need to check drill sizes of each size bolt. Drill sizes are the sames as bolt sizes, for example: 5mm = 5.0 Drill Bit, 6mm = 6.0 Drill Bit etc. Please be aware that there are inferior self tapping masonry anchors on the market.