The early "screw" mechanisms for sealing the breech consisted of threaded blocks which were screwed tightly into the breech after loading, but the threads themselves were insufficient to provide a gas-tight seal. This was further complicated by the need to screw and unscrew the breech as quickly as possible; this was met by the "interrupted thread" breech block, where the block circumference was alternately threaded and left unthreaded at a slightly smaller diameter to allow the whole block to be fully inserted and rotated a fraction to lock it. Hence if the block circumference was divided into two sets of threads and gaps, the block only needed to be rotated ¼ turn to lock it instead of several turns. The tradeoff was that only ½ the block's circumference was threaded, reducing the security accordingly.