attofarad

The original bulb in my Hartenberger Nano is an Osram 6V 20W part, which may be this same one (I don't recall the part number). It can be found for $2-$3, so no reason to pay $20.

I have a Hartengberger Nano, which I picked up used with just a few dives on it. Very uniform diffuse lighting, 4 levels of brightness, and can use either the 20W or 10W bulbs. Nano

I think I've read of someone cutting sections of thin small bicycle tubes, and slipping those over the their balls. I'm not sure how well or for how long that will work, but it is cheap to try. I haven't put my Aquatica TLC arms into use yet, but they have no o-rings, and people seem to like them.