Hi Kat, if you get a chance to measure them, please do so - normally we have M6 x 28mm screws, you may have gotten the M7x 28mm version, which was an interim solution as at the time we had some issues with inserts stripping (only later did we find out that it was due to a recycled plastic that did not have 100% consistency) - I am surprised though that you say the new strap with the thicker screws work on the newer board. Anyway then you need to open the holes very slightly with a bigger drill bit of size 5mm (for M6 screws, a drill bit of 4.2mm is needed).
Obviously please measure the distance of the screw underneath the strap, to see how long it is, then you know how deep the screw needs to go inside. And then tape the drill bit accordingly to length, to make sure you do not drill it too deep.
Would be interesting to hear if the straps/screws from your FreeWave fit into the Blast - if so, then you could just switch them, since the Blast straps/screws fit into your Freewave (at least that is what I understood above?)
Good luck, let me know if not clear above, we had a really tiny amount of boards with this problem, is an easy fix at a shop/centre, obviously for you more complicated?