Bloc - Loc rulers for HSTs. Two thumbs up.
 

Just opened mine 2 days ago and used it to square up some oversized HSTs. OMG. That, paired with my rotating mat, made this job SO MUCH easier. The squares came out perfect and it was so fast and easy. Highly recommend. I might have to invest in the flying geese ones too.

I won set of the Bloc Loc rulers on a blog giveaway. I use them and recommend them.

I love love my bloc loc rulers, the flying geesebrulernis my favorite

I haven't been able to use mine yet, but DH gave me a 6.5" square one for my birthday. He had taken me to a LQS, the first time I'd been there in a couple of years, when I spied "new to me" rulers. The owner gave me a little demonstration and the ruler followed me home! - Along with a Laundry Basket Quilt pattern and template for "Eldon."

I love mine for hst's they make my life so much easier. I've not tried the flying geese one I imagine it's pretty awesome too.

Pricey but worth every penny!!!!! Love mine. I also second the comment about the rotating mat. These tools paired really helped improve my squaring up speed and accuracy.

WOW just looked at the set for $88. Little pricey for my budget.

I bought a set at Paducah a few years ago--it has the 2.5, 4.5 and 6.5 half square triangles and I love them. I also bought the flying geest (finished 3x6) and use it a lot. I have the 9.5 half square triangle ordered now for a quilt I want to do. I love that they hold and don't slip. I am doing a class at my local extension office and tried to show the half square triangle to the instructor and she didn't even want to consider it. She told everyone there was no need for specialty rulers when the ones you had have the 45 degree angle on it (sure they do, and they can slip very easily too!). The ruler got passed away anyway and I noticed quite a few people were writing down the website for BlocLoc. I know they aren't cheap but I am a gadget person and love tools that make things easier to do and very accurate!

I went to the Bloc-Loc site and watched the demo. It seemed you could use the HST square up ruler for several sizes then when I looked at the ruler sale area there are many sizes. Can you purchase the 9.5 size and use it for 9 inch blocks and smaller? I don't understand why you would have to buy one for every size block?

I used a 6.5" one to square up 3" blocks. Easy as pie. I might get one larger one and I think between the two, I'd be set for any size HST. I was also able to use my Eleanor Burns 3 x 6 flying geese ruler to trim my 2.5 x 5 flying geese. I just had to use the one side to get the "point side" just right and then used a ruler for the rest. Having that angle printed on it really helped me to trim the point side just right.