Our Larval Engineer practiced fencing for several years, learning the fundamental truth that you should always bring a gun to a knife fight:
It’s time to pass the gear along to someone who can use it, but we discovered one of the ear grommets inside the helmet had broken:
The cylinder in the middle should be attached to the washer on the left, which goes inside the helmet padding. It’s a tight push fit inside the washer on the right, which goes on the outside of the padding. Ridges along the cylinder hold it in place.
Being an injection-molded polyethylene part, no earthly adhesive or solvent will bother it, soooo… the solid model pretty much reproduces the original design:
The top washer goes inside the padding against your (well, her) ear, so I chamfered the edges sorta-kinda like the original.
There are no deliberate ridges on the central cylinder, but printing the parts in the obvious orientation with no additional clearance makes them a very snug push fit and the usual 3D printing ridges work perfectly; you could apply adhesive if you like. The outside washer has a slight chamfer to orient the post and get it moving along.
The posts keep the whole affair from rotating, but I’m not sure they’re really necessary.
Printing a pair doesn’t take much longer than just one:
It doesn’t look like much inside the helmet:
The OpenSCAD source code as a gist from Github: