Cap hole is 9.2mm, should hold most/any XL carto. It seems the flanged F16 cartos are ever so slightly smaller ID than others. Unfortunately I don't have any ST's handy; but I just measured some other feeds, they're 0.1 - 0.2mm larger (F16 8.5mm, Vivi was 8.7 and HH357 was 8.6). Enough of a difference to make half my tips not fit at all. I'm sure different ORings can solve most of this trouble, just hate pulling them off n on, tis a pain.