You do not own one "Leica filter size." You own a thread diameter. In the Leica world that shows up most often as 39mm, 46mm, or 49mm on the Q3 43. Buy the millimetre on your barrel. Do not buy a "Leica kit" and hope.

I'm Leo Liang. I run XT Filters. Wrong-size returns still land here with rings that never caught a thread. Most of those mistakes start the same way: someone treated the focal length, the model name, or a forum shorthand as the filter size.

M and Voigtlander: often 39mm

A lot of Leica M glass and Voigtlander M-mount lenses take a 39mm screw-in filter. That is the common small rangefinder mouth. If your front ring (or the lens chart) says ø39 / E39, shop 39mm. Not 43. Not "close enough."

This is where a slim black UV that still clears a hood matters. Our XT995PRO is cut as a slim black UV with a custom 39mm frame for rangefinder use ($44.99–$89.99 by size). The point of that cut is simple: protect the front without fighting the hood you already own.

Some Leica lenses: 46mm

Not every Leica-world lens is 39. Some take 46mm. Same brand family, different mouth. If you already own a drawer of 39mm glass and you pick up a 46mm lens, the old stack will not rescue you. You need a second diameter.

We cut Leica 46mm on the XT996 PRO black-frame protection line ($64.99–$179.99 by diameter). Pick the 46mm listing for that lens. Do not order 39mm and plan to step-ring your way out of a mismatch on a tight nose.

Q3 43: the working thread is 49mm

The Leica Q3 43 does not take a 43mm filter. The "43" is the focal length. The filter thread is 49mm (E49).

I already wrote the parking-lot version of that trap, including the factory square hood and macro travel, in a separate note: Leica Q3 43 filter size is 49mm. The short version you need before you click buy:

  1. Order 49mm, never 43mm.
  2. Ask whether you keep the factory compact square hood.
  3. Ask whether you use macro travel with a filter on.

Leica's own compact hood and a filter do not play nicely together on that nose. Generic 49mm frames often foul the hood. We cut a dedicated 49mm(Q343) frame on XT996 PRO. We still will not promise that every factory-hood-plus-macro combo clears without a hand check. If that hood-plus-macro combo is non-negotiable for you, test clearance before you torque anything down. If you drop the factory hood, a true 49mm protector or mist is a cleaner path.

For mild diffusion on that same 49mm mouth, the XT888 Bottom 1/4 ($49.99–$119.99) is available in the Q3 43 49mm cut. That is a creative choice, not a substitute for reading the thread first.

How to check before you buy

Read the front ring for ø / E plus a number. If the ring is under a hood, twist the hood off and look again. If the print is gone, open the current lens PDF or the maker's filter-diameter line — not a random shopping title that says "for Leica."

Then match that number to one shopping cart:

  • 39mm rangefinder / M-Voigtlander path → XT995PRO for slim UV, or XT996 PRO in its Leica 39mm cut for black-frame protection.
  • 46mm → XT996 PRO in the Leica 46mm cut.
  • Q3 43 → 49mm only, then decide hood and macro before you commit.

Three threads. Three filters. One bag can hold more than one diameter if your kit does.

Email me the exact lens (and whether you keep the Q3 factory hood) if the page labels look ambiguous. Or shop XT995PRO / XT996 PRO in the millimetre you actually measured.

— Leo Liang