Derailleur hanger is a metal extension of the rear dropout through which a rear derailleur is mounted. If the rear derailleur is damaged, mostly likely the derailleur hanger could be damaged as well and has to be replaced. Its also recommended to carry a spare derailleur hanger when riding a mountain bike.
Below is a reference of compatibility list. On top of that, please always compare the geometry of your original derailleur hanger with that in the picture to make sure you are purchasing the right part.
Compatibility Reference:
(Note: because bike manufacturers keep bringing new models to the market, some models may not be listed here. If your bike is one of these brands below and the derailleur hanger looks identical to the listing picture, its very likely to fit)
Replacing parts no. #4021, #4020
SPECIALIZED:
2017-2019 Ariel Series
2007-2011 - Big Hit Grom Hit FSR
2006-2011 - BigHit FSR
2011 - Camber
2012 - Camber 26" (Elite/Comp)
2012 - Camber 29" (Base model)
2012-2013 - Carve 29"
2017-2019 Crosstrail Series
2007-2010 - Demo 7
2005-2010 - Demo 8
2010-2011 - Enduro
2014-2016 - Fatboy, Fatboy Trail, Fatboy Comp
2012-2015 - Fate 29"
2017 Fuse 6Fattie
2018 Fuse 6Fattie/29
2018 Fuse Sport 6Fattie/29
2011-2015 - Hardrock 29"
2011-2015 - Hotrock 20 Street / 6spd
2011-2015 - Hotrock 24 Street / 21spd / 7spd
2012 - Jett 26"
2012-2014 - Jett 29"
2011-2015 - Myka HT 29"
2013-2014 - P.Street
2008, 2011, 2015 - Pitch
2006-2010 - Rockhopper HT
2005 late - Rockhopper HT
2011-2015 - Rockhopper M4 26"
2011-2015 - Rockhopper M4 29
2011 - Rockhopper M4SL 26"/29er
2010 - Rockhopper Comp 1X
2010-2013 - S-Works Carbon HT 29"
2014 - S-Works E5 HT 29
2006, 2010-2011 - S-Works Enduro
2009-2012 - S-Works Era
2013 - S-Works Fate Carbon 29
2012-2013 - S-Works HT 29"
2018 Sirrus Mens Alloy
2018 Sirrus Mens Sport
2018 Sirrus Womens Alloy
2012-2015 - Status
2014 - Stumpjumper 29er HT Alloy
2006-2011 - Stumpjumper FSR
2008-2012 - Stumpjumper M5 HT
2007-2012 - SX
2007-2010 - SX Trail