Photographic filter holders are usually metal. Looking for a source of plastic ones, to avoid corrosion.

Need is to hold diaphragms instead of optical filters. Can be from any application other than cameras.

 

Sample pictures ----> https://www.aliexpress.com/item/NEW-Camera-Filter-40-5-43-46-49-52-55-58-62-67-72-77-82mm/32655570830.html?ws_ab_test=searchweb0_0,searchweb201602_4_10152_10065_10151_10068_10130_10084_10083_10080_10082_10081_10110_10178_10136_10137_10111_10060_10138_10112_10113_10062_10114_10156_10056_10055_10054_10059_10099_10078_10079_10103_10073_10102_10096_10070_10148_10123_10147_10052_10053_10124_10142_10107_10050_10143_10051,searchweb201603_1,afswitch_1,ppcSwitch_5&btsid=146df83c-95b6-4753-b2d1-3cda58aa911c&algo_expid=c850960c-3731-4b5a-af29-60e21c040383-16&algo_pvid=c850960c-3731-4b5a-af29-60e21c040383

The examples you show are aluminum and shouldn't corrode.

They will corrode undersea. Looking for plastic equivalents. Link was example of shape/construction/purpose.

If you cannot find any, you can ask a machining workshop to make them for you.