Stretcher frames and strainer frames are often used by artists, painters and embroiders.  These frames are the wooden framework which hold and support the canvases artists paint or create.  Embroiders sometimes also use these frames for their embroideries since these  can provide the durable tensions needed for sewing and pinning.  That said,  the greatest difference in Strainer Frames Versus Stretcher Frames is the cost.   You can buy online a 50x75 cms (20”x30”)  stretched, primed ready-to-paint, canvas stapled to a strainer ..