I have a "notion"
 

June Tailor 10-1/2-Inch-by-12-1/2-Inch Perfect Half-Square & Quarter-Square Triangles Ruler

I've been repeatedly informed that I can use this tool to cut 10 1/2" squares out of which I can make the above-mentioned triangles. Slots on the ruler go up to 6 1/2". I do understand that I can make 6 1/2" squares and then small triangles. I have been thinking since the beginning of last month and still lack that Eureka moment when all becomes obvious regarding the larger measurements. How might my goal be practically accomplished with this tool?

I love gadgets... have fun with yours!

There are directions on the website, but since I don't have the tool, don't know how useful they are.

I was told by various customer service reps at Fabrics.com that I could accomplish the 10 1/2" square by using the outer line on the tool. I ordered the item in the hopes to make triangles from 10 1/2" and also 12 1/2" squares.
I kept asking for a return of the item, and they kindly kept sending me the same item type back.
As far as June Tailor, I did watch a tutorial for a similar tool, and I called by phone twice. On the first call I was treated poorly; the representative talked down to me from the very get go. I'm new to quilting, and this has really has me stumped. I waited several weeks and attempted to reach them again; no return call after several days.
I was hoping someone on this site might have this notion, which is also being sold on Amazon.com

If the tool measures exactly 10.5" in one dimension, then you could use that dimension to measure and cut your 10.5" squares, but you probably already figured that out. I don't have the tool (and don't buy June Tailor products in general because of 2 bad experiences with them) but from looking at it on the amazon site I don't think that it would work in the way it is meant for marking the sewing lines all the way down the diagonal of the 10.5" square. You really don't need a special tool to do any of this anyway. Just use a "regular" ruler and you'll be just fine.

Here's the link to the instructions on the June Tailor website:
http://store.junetailor.com/store/p-...les-ruler.aspx

Under the picture, there is a small #2 - click it and you'll see the steps using the ruler.

Meh.

That ruler is not large enough to use for cutting or marking the lines needed to make HST blocks from 10.5" squares. You'd still need to extend the lines.

Save yourself $24 and learn these 2 methods - all you have to do is remember 2 simple formulas, and you'll be able to create ANY size HST and QST blocks you want/need.

HST blocks
http://quilting.about.com/od/quickpi...uaretria_2.htm

QST blocks
http://quilting.about.com/od/quickpi..._squares_2.htm

Keep in mind that most of us that use these methods tend to cut the starting squares a bit larger than needed, and then trim them down to the exact UNFINISHED size needed.

Many lament the extra step, but I don't mind at all - it's a pleasure to then use these units to make incorporate into larger blocks/quilts patterns.

Thanks so much, ladies, for your informative replies--which were very helpful.

HSTs come up alot.
After years of trying different methods even wasting $23 on Triangulations, which uses paper grids, I find that Eleanor Burns method is by far the best. Quilt in a Day triangle square up ruler is at Joanns and with a coupon it is less than $10.
You do need her triangle square up ruler, it is the best tool I have. With it you can square up with just one cut.
For making 8 HST at a time you use two squares right sides togather. For 2 1/2 in squares use two 6 in squares. Just add two inchs for the next size up. 8 in for 3 1/2 in squares etc.
Just draw an x on the sq then sew 1/4 in down each side of lines. Cut the sq in half each way then on drawn lines to get 8 HSTs. Then with the ruler make one cut to square up.

yup, leave it to E.Burns to make quilting fun. I think because of her pioneering her quilt in a day theory so many of the gadgets we have today were born........