Recently certified as a rear cord safety device for roman blinds   For use with 4mm fibreglass rods. 
 
Comes away under pressure - reusable -  clips back on
 
Clear Clip Ring Roman Blind Safety Device - for 4mm Rod - Child Safe
 
Roman Blinds Spare Parts - Rear Ring and Clip for 4mm Rods
 
Sold in packs of 10 - 20 - 25 - 50