Old Exachrom filter set marked 'Leica'

I have a set of filters (dark red, red-orange, yellow, green) in a

small box (probably made of cardboard). The box (with tissue/velvet

liner inside) is marked 'Exachrome' on the inside of the top cover. On

the outside of the top cover there is an embossed marking 'Leica'. The

filters all have 36mm thread diameter (measured with a caliper). Does

anyone know anything about these filters, and which (Leitz) lenses

they will fit?

 

Some noted the french words 'jaune 2' and 'vert 4' on the inner liner,

designating filter color and factor. Does this point us to a french

origin?<div></div>

The hand-written french just makes me think a previous owner was French/Swiss/Algerian etc.

Third party ( Exachrom ) made. Classic colors for black and white and either a blue or infrared.

 

They fit 3.5 50mm elmars, 50 summar, 90 4.0 elmar, 135 4.5 amd 35 3.5 elmars. These lenses take what is commonly called 36 mm accessories. Whether they actually are threaded, I would have to check my samples.

Third party ( Exachrom ) made. Classic colors for black and white and either a blue or infrared.

 

They fit 3.5 50mm elmars, 50 summar, 90 4.0 elmar, 135 4.5 amd 35 3.5 elmars. These lenses take what is commonly called 36 mm accessories. Whether they actually are threaded, I would have to check my samples.

Early Leitz lenses with 36mm flanges, if they were threaded at all, took 34mm threaded filters; but most early lenses were designated for the A36 push on or clamp on filters or other accessories. Filters with 36mm diameter threads would require some kind of adapter which I have been unable to find in any of my references, except by third parties. My 90 Elmar has threads that are 34mm but I believe they weren't intended to accept filters but for the lens bezel. Walz provided screw-in 34mm filters that would fit these threads. AFIK the 90 Elmar and 135 Hektor were the only Leitz lenses with these threads. Some Summars might have had 34mm threads.