Regular fragmentation grenades were ineffective against tanks, so many kinds of anti-tank grenades were developed. These ranged from hollow charge designs (e.g., the British No. 68 AT Grenade), to ones that simply contained a lot of explosive (the British No. 73 Grenade). To increase their effectiveness, some grenades were designed so that they adhered to the tank either through an adhesive (sticky bomb) or with a magnet. The Germans used a magnetic grenade, the Hafthohlladung to ensure that the shaped charge would fire at the optimal 90° angle to the armor.