Today I had a local glass-replacement shop make me a 16.5" square of 1/8" thick acrylic, the same thickness of my Omnigrid rulers. It's precise, smooth-edged, and cost much less than ordering one this size that doesn't seem to be stocked ordinarily. Of course it doesn't have the lines like a 'real' quilting ruler but I'll put the size & diagonal lines & 1/4" seam lines on it and then cover that with the clear non-slip stuff to keep the markings from coming off.
I'll only use it for squaring up the big blocks & batting & backing for the quilt-as-you-go I'm working on ("Buggy
Wheels" 16" finished blocks. There are several pictures if you "Search" in the options listed at top of this page).
Much easier than having to measure several times for each component.