What size should I use for a 36 -11 casette?

Forgive me, but you are asking the wrong question.The cage size is controlled by the maximum amount of slack chain created by the combination of chain rings AND cassette. This is called "Chain Wrap".To formula for chain wrap is (Big Chain Ring - Small Chain Ring) + (Big cassette Cog - Small Cassette Cog). So if you are using a compact double chain ring (50-34) and a 11-36 cassette the numbers work out to (50 minus 34) + (36 minus 11) or 16 + 25 = 41. This means that if you shift from a big-big combination to a small-small combination, your derailleur has to be able to handle 41 teeth of loose chain, which calls for a long cage. On my bike a have a single 40 tooth chain ring and a 11-42 cassette so the chain wrap works out to (40 - 40) + (42 - 11) = 0 + 31 = 31. So even though I have a huge cassette I only need a medium cage because I have no front derailleur to create more chain wrap.Hope that helps.

what is short, medium.long cage?

It has to do with chain wrap capacity. Small=30t Chainwrap Capacity, Medium=35t, Long=47t. The wrap is just the difference between the number of chain ring teeth plus the difference between the cog teeth. For example a 53/39 with a 12-25 cassette requires 14 + 13 = 27 teeth of wrap capacity needed from the RD.

Will this work with Shimano Ultegra shifter

No, actuation will only work with sram.... The good news is that it will work with both sram 10 speed road and Mtb... Unlike the newer 11 speeds witch are road or mtb specific.

Can this be used with a shimano 11/42 cassette ?

I used it with a sunrace 11-42 cassette but I needed a longer b tension screw(which was not provided) so you will likely run into the same issue.

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SRAM GX Type 2.1 Rear Derailleur - 10-speed

Product ID: 20172372

Details

Brand
SRAM
Color
Black
Item Weight
157 g
Material
Aluminum
Mounting Type
Standard

⚙️Exact Actuation tech for zero slack

🛠️Lightweight 302g aluminum & steel build

🚵‍♂️Direct Route Tech for effortless shifting

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Description

🚵‍♂️ Shift into the future — flawless control, every trail, every time!

BUILT TO LAST - Engineered for rugged off-road conditions, combining longevity with consistent, reliable performance.
PRECISION PERFECTED - Exact Actuation technology eliminates slop and ensures razor-sharp 10-speed shifts every ride.
CLIMB WITH CONFIDENCE - Direct Route Technology delivers smooth, light-effort shifting even on the toughest ascents and descents.
FEATHERWEIGHT DURABILITY - Crafted from high-strength aluminum and steel, weighing just 302g for peak performance without the bulk.
TRAIL READY COMPATIBILITY - Long cage design supports up to 36T gears and 47T chain wrap capacity, ideal for all-mountain and enduro riders.

The SRAM GX Type 2.1 Rear Derailleur is a 10-speed, long cage drivetrain component designed for mountain biking enthusiasts seeking precision and durability. Featuring Exact Actuation technology for zero slack shifting, a lightweight yet robust aluminum and steel construction at 302g, and SRAM’s Direct Route Technology for effortless gear changes, it supports a wide gear range up to 36T and a chain wrap capacity of 47 teeth. Perfectly suited for all-mountain, enduro, and trail riding, this derailleur delivers reliable, high-performance shifting in demanding off-road conditions.

Specifications

ASIN	B00V8RZ9SW
Best Sellers Rank	#91,892 in Sports & Outdoors ( See Top 100 in Sports & Outdoors ) #44 in Rear Bike Derailleurs
Brand Name	SRAM
Case Material Type	Aluminium
Color	Black
Customer Reviews	4.4 4.4 out of 5 stars (745)
Global Trade Identification Number	00710845771835
Included Components	Rear Deraille
Item Dimensions L x W x H	12"L x 8"W x 2"H
Item Highlight	SRAM GX Type 2.1 10-Speed Long Cage Rear Derailleur - Clutch Technology
Item Type Name	SRAM derailleur gx type 2.1 long cage 10 speed black
Item Weight	157 g
Manufacturer	SRAM
Manufacturer Part Number	00.7518.080.000
Material Type	Aluminum
Model Number	00.7518.080.000
Mount Type	Standard
Number of Items	1
Number of Teeth	10
UPC	757183591480 710845771835 784427964175
Warranty Description	Limited Warranty

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HK$1034

Duties & taxes included

In stock

Sold byAmazon Hong KongDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

Desertcart purchases this item on your behalf and handles shipping, customs, and support to Hong Kong.

Secure transaction

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