There is no actual measurement for a "scant 1/4 seam". What really matters is the final finished measurement of the block after it is sewn. For example, most of us cut a 2.5-inch square if we want the final finished measurement to be 2 inches square, now if you are using a heavy canvas material, you might find you need to make a skinnier seam as the fold made while pressing will take up more of the fabric than using a sheer material where you might need to take closer to an actual 1/4 inch seam. The thickness of the thread you use, also effects that actual seam amount you need to take. Best way is to stitch some practice pieces of very similar material and thread and then measure them. There are video's how to do this. For raveling, I haven't had much problem with even a scant seam as I use the more tightly woven quilt shop quality cotton, reduce my stitch length to 2.0 or lower on my Bernina. and make sure I edge stitch around big blocks or the entire quilt to make sure the ends of the seams do not come apart. If you have a very loosely woven fabric, you may need to take a bigger seam or edge finish the seam allowance. This would be tedious on a large quilt and you would have to recalculate all the pieces you need to cut to adjust to the larger seam allowance. Normally, as I am using quality quilting fabric, I have no problems with seams raveling even if I get down to an eight of an inch. I do my own quilting and will do a dense quilting design if there are many, many small pieces and lot of seams. They have held up during machine washing and machine drying.