Its the other one , offset bushing for big hole upper to small hole lower.
Found 2 sources $17&$20 shipped.
I will sell the upper before I pay $15 to ship a $3 part
Like this , im just not paying $14 for shipping and the 2 sources I found do not have anything else im interested in to offset the shipping.
COLT OFFSET BUSHING OFF SET ADAPTOR ADAPTER
www.jsesurplus.com