The R3 clutch size has been discontinued by Rollease. However, the R8 is a direct replacement for it. 

The R8 clutch will work with your existing tube, shade, and mounting brackets.

This genuine Rollease replacement clutch mechanism fits into a 1” wide round metal tube. It raises your roller shade up and down with a metal or plastic bead chain or a continuous cord loop.

Features:

• - Fits into a 1" (outside diameter) metal roller shade tube.
• - The maximum shade weight is 9 pounds.
• - Uses #10 metal or plastic bead chain or a C-30 cord loop.
• - Made by Rollease, the industry expert in roller shade technology.
• - Rollease part numbers R3C02, R3C02W & R3C02BK have been discontinued. These are directly replaced with R8 clutches.
• - Part of the R-series of clutches, the #1 leader in reliability, dependability & strength.
• - Instructional guides for repairing roller shades are available here. 
• - Available in black, white and natural.
• - Sold individually.