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 have a responsibility to students they serve to identify their needs and implement instructional strategies to scaffold students’ understandings of sounds. Intervention strategies may be necessary in remediating students who cannot correctly identify sounds in isolation on a given opportunity. Programs like Reading Recovery have contemporary phonemic techniques embedded in the program. Also, books and poems may specifically focus on word families and similar sound patterns for children to identify and understand in context. Sound sorts can be integrated through programs, or very inexpensively through teacher-created materials. For example, students can sort pictures by beginning sound, rhyme, or ending sound.