I have a nice set of matched 18mm with eye lenses that are a whopping 2mm, as large as any of my Naglers barring my 20mm; I believe they are Russel Optics. They are not threaded for filters nor are they capped.
They are a sight to see through when in my binoviewers; nice, bright, sharp, and contrasty with room to look around. These are very nice eyepieces and are practically brand new I just have too many of them. That's only (($50.00 Shipped)) in the cont. USA ((SALE PENDING))
Thanx for looking, Drew