Apart from ATCs, other formats that are being traded over at the ATCsforAll.com forum are inchies (1″x1″), twinchies (2″x2″) and chunkies (4″x4″). The latter is the perfect format for these beautiful stamps:
I stamped them using versamark clear ink on colored cardstock, then embossed with white embossing powder. I used semi-thick 3d tape bits to attach the 4 top squares onto the bottom white layer, and attached those to the colored cardstock base using thinner 3d tape. I can’t remember by heart who made these stamps, but can look it up in case someone likes to know!