DIY Interlocking LEGO Heart Pendants. You can buy the Coupling Plate 2X2 or design ID 3176 (official lego name) various places like here for $.17, shipping $4.95 or this looks like a place to try here: http://www.bricklink.com/catalogItem.asp?P=3176. Other suggestions in the comments’ section. Tutorial from Instructables here.
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