Derailleur gears several standards in use, and in each the product of the derailleur's actuation ratio and the length of cable pulled must equal the pitch of the rear sprockets. The following standards exist. Some rear derailleurs, especially for mountain bikes, incorporate a clutch to keep the lower length of chain in sufficient tension to prevent the chain from striking the bottom of the chain stay, called "chain slap", and which can damage the chain stay. Clutches are also helpful in preventing the chain from derailing from the chain ring on systems without a front derailleur. The front derailleur only has to
Word sort - their spelling or orthography - the more efficient and fluent their reading will be. Word sorts place instructional emphasis on the exploration of patterns that can be detected in the sound, structure, and meaning features of words. Thus, word sorts contribute to orthographic or spelling knowledge, the engine that drives efficient reading as well as efficient writing. There are three different types of word sorts: sound sorts, picture sorts, and word sorts. Sound sorts can take on many forms in a primary classroom and this is essential because sound is the first layer of English orthography. Sound study can