which rear derailleur do i need ??

[cyberstretch]

Hi all

I cant believe that all i knew as a teen when it came to bikes has fizzled away from my memory banks !
So i need some help please if someone can assist.

I have just fitted new brakes,lever,twist gears and all cables to my daily commute 21 speed hybrid and i want to change the now old and battered rear derailleur. I have looked and there are lots to choose from, long reach, short reach and ones with min and max teeth requirments - its all very confusing !

I am looking for a non expensive standard r/d to do the job. I saw a tourney RD-TX35 that seemed like it would fit but im not sure.

thanks people

 

[subaqua]

what was on it originally ?

 

[cyberstretch]

This is the tired looking item and definitely in need of a change . Not sure what I would be looking at in order to match if up with a nice new replacement

 

[Hacienda71]

That looks like a Shimano Altus although I might be wrong. So in theory most Shimano 7 speed mountain bike mechs would work fine. It isn't cracked is it?

 

[cyberstretch]

Its not cracked, I thought that I would change it as I have just replaced the brakes and twist gears and its looks like its been on the bike since new. Part of my updating the bike