That's one of those F&G Conversion bags, they do not use Kirby bags, but Eureka type F&G bags (Electrolux type E74 for us in the UK), they don't work as well as the original Kirby setup, plus they really look ugly on a Kirby...
It's best to keep the F&Gs on Eurekas and Sanitaires where they work properly, than to fit them on a Kirby where they don't work as well... 
Link to Electrolux's online store for E74 bags:
[URL unfurl="true"]http://shop.electrolux.co.uk/node544.aspx?wscid=21&wssubcid=30&wspartno=9001952002[/URL]
