14-28T Model: MF-TZ20 / MF-TZ500-6 14-34T Model: MF-TZ21 / MF-TZ500-6 Speed: 6 Speed Type: Freewheel Mount type: Screw On(Theard type) Compatible chain: UG/HG "MF-TZ20" and "MF-TZ21" are the old model of "MF-TZ500-6",same design and material,random ship out 14-28T Model: MF-TZ30 / MF-TZ500-6 14-34T Model: MF-TZ31 / MF-TZ500-6 Speed: 7 Speed Type: Freewheel Mount type: Screw On(Theard type) Compatible chain: UG/HG "MF-TZ30" and "MF-TZ31" are the old model of "MF-TZ500-6",same design and material,random ship out Generally 14-28T fits folding bike and road bike,14-34T fits MTB bike. Shimano MegaRange system gives you a super-low 34T gear to help you tackle steep hills with ease. Hyperglide gear sprockets are engineered for smooth chain movement up or down the block. This freewhell can be easily installed onto compatible screw-on type hub. It suitable for mountain bikes and a wide range of other cycles.