Schneider Push-On Lens Cap (58mm)

As the Olympus C-210 teleconverter has been discontinued and is no longer available, and I see no specifications listed for the unit online, I would simply have to recommend to measure the outer diameter of the teleconverter in millimeters (or convert your available measurement into millimeters). If the outer diameter measures between 56-58mm, then it should fit. If not, you would have to find the size that is equal or slightly larger than your outer diameter measurement.

The Schneider 86mm Push-On Lens Cap will not fit on the B+W XS-Pro Digital ND Vario MRC-Nano Filter (82mm, 1 to 5-Stop ), which has an 86mm front thread size; the Schneider 90mm Push-On Lens Cap (SCLC90) will fit.

Yes, the Schneider 25mm Push-On Lens Cap can fit over a Heliopan 24mm UV filter mounted on a Rollei 35 Tessar.

For the Tiffen Variable ND filter (82mm), the Schneider Push-On Lens Cap (100) will not fit. You need a 95mm lens cap because its front filter size (accessory thread) is 95mm.

The Schneider 86mm Push-On Lens Cap is like most any other lens caps listed as slip on. This is an image of the back side of the lens cap, https://bhpho.to/41aBHDW.

I'd measure the outside diameter of the the step up with something accurate like vernier calipers or a micrometer. I purchased the 90mm push on Cap to fit a Schneider centre ND filter which I measured to be exactly 90mm outside diameter and the cap was a fairly tight fit.