Does anyone know these filtercassettes

[L´Andratté]

I just bought them and am curious about what they are.
Called low pass, hi pass and k112 band pass audio filters. No further information.
Was cheap and worth it in parts anyway (nice inductors) but also nice
if it could be turned into something useful, because I like these old cassettes.
Looks like old telephone/broadcasting stuff or crossover filters.
Really no clue. Thanks!

http://abload.de/image.php?img=bandpass-filterl8rkl.jpg

http://abload.de/image.php?img=bandpass-filters24qi5.jpg

http://abload.de/image.php?img=hochp.tpivxpcv.jpg

http://abload.de/image.php?img=hochp.iqjqz6.jpg

http://abload.de/image.php?img=tiefpv.ivaqcs.jpg