This is a stretch artist square canvas. 12x12 in size.
Custom Made Canvases
Stretch Artist Canvas Rectangular Large
Shop Stretched Canvases & Screens online at Modulor
extra large canvas art, extra large wall art canvas L296 – LargeArtCanvas
Painter's Reference: A Guide to Common Art Canvas Sizes
How to Build a Custom Sized Stretched Canvas : 10 Steps - Instructables
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How to make a stretched canvas from start to finish- Artist Tutorial –
DIY Project: How to Frame a Stretched Canvas Painting - FeltMagnet
Stretch Canvas: Prime Art Blue Label (Boxed Profile) - Prime Art