Shimano Tourney RD-TY500-SGS Rear Derailleur

This is the latest, lower end straight-pull Tourney & replaces the RD-TX55, TX-75 straight pull RDs for 6 and 7 cog freewheels - usually 18 & 21 speed bikes. Also works with 34T Mega freewheels. Straight pull tech trickled down from the higher end Shimano Shadow stuff. This means the RD cable runs along the seat stay directly to the derailleur without the cable loop in the back. Note the cable termination is pointed up in the photo. You an find these for around $15-$20 & are a great replacement on any budget bike. They're particularly good if you do off road riding since there's no cable loop to snag, sticks, brush or debris, possibly bending the steel hanger or pulling the derailleur into the spokes. The next level up in the Shimano line is the Acera but it doesn't offer a straight-pull design & is meant to be bolted to a replaceable derailleur hanger (does not include the steel hanger attached to the Tourney series). My only gripe about the lower end Shimanos is the cable's pinch bolt setup. I've always had trouble with these. How 'bout spending an extra penny for a hex head at least, Shimano? Anyway, the pinch bolt system is the same on all of them until you get to the Alivio & Deore line.