hst's ?
 

to have a finishd size is 3.5 " what size squares do you need to cut? i used to know but my brain is on vaca right now.

For the exact measurement, you would need to cut the starting squares at 4-3/8".

But the method I prefer, fwiw, is to cut them larger, make the HST locks, and trim those down to 4" UNFINISHED.


(you always have to add at least 7/8" to the FINISHED HST block measurement to get the starting square size

while we're here, the measurement for the starting squares for QST blocks is 1-1/4" (at least) added to the FINISHED block size.

Again, I prefer to cut larger and trim down.)

I agree with MTS, however I would start with 4.5" squares, because measuring that eighth of an inch difference would drive me nuts. This gives you a teeeeensy bit of extra to trim, which (like MTS) is also MY preferred method. Do a practice block cut at 4.5" and see how it turns out. If that's too small for your comfort, bump it up to 4.75".

If your 1/4" is reliable, you can cut 4 1/4" and still have some to trim. I've done only a half inch extra called for in a pattern, but it was not fun. I add 3/4" now.

FYI - the latest notion to address the HST block trimming issue is the BlocLoc ruler, which was FLYING out of the booth at Houston -

http://www.blocloc.com/

I did not buy it (because I don't find it a hassle with my existing square rulers).

Others here have said they love it.

YMMV.
NAYY.