These brushes match the original soft brushes for Roomba 5, 6 and 7 series, but are more durable. The brushes printable from here rely on axles from the original brushes, so don't discard worn brushes, just strip the foam and keep the axles. Pull on the new sleeves from TPU (see image). You may keep the original spacers/inserts, or print new ones.

The image above shows a stripped axle (the hex-ended kind in this case). The spacer inserts are visible – the green one is original, the blue one is 3D-printed from STL available here. Note the arrow. You need to pull the new brush on the axle in that direction. Note that you need to remove the intervening spacer (green in this case) before, and replace it after.

TPU prints nicely bottom-up. You don't need skirts, just print as is (bgcode included). I have been running my first set on my Roomba i7 for half a year now, and although there are signs of wear, they are still in top shape – see photo on the right, that's after seven months on an every-working-day schedule. While the originals get cut in half by a few hairs, there's barely a spot o these sturdy ones. The only downside: they are noisier so schedule your vacuuming for when you're out.