Ok, I know it's an old thread, but it keeps being linked to when there is a discussion about using 220 inserts with 120 film.
I have both inserts and
they are, in fact, different! Somehow it's not immediately obvious even when you look at them side by side, but 220 pressure plate has different thickness to accommodate for the lack of backing paper on 220 film. Although it may have no noticeable effect on the IQ, it has other implications to it. If you mod a 220 insert as outlined above and run a 120 roll through it you will immediately notice that the motor sounds different compared to using 120 film in 120 insert. This is because
using 120 film in 220 insert puts more strain on the camera motor. This may wear the motor down faster, break it altogether or harm the camera in some other way we don't and can't anticipate.
This claim is supported by Eric, whom I contacted some time ago to seek his expert opinion on the matter:
Quote: The 220 film hold is made a bit different to hold the film tight to the format opening so it isn't loose. So when you put the two layer (120) film on a 220 holder it will put pressure on the motor to pull it through. So don't do it.
So yeah, don't do it.
That said, you can probably use a 220 insert in a pinch, but please understand, that you will likely be actively participating in your 645's untimely demise this way. Whether running down a perfectly good camera is worth the price difference between 120 and 220 inserts is up to you, but my personal opinion is it's not.
I'll post photos showing the difference between the inserts later.