Cerumen Filter from Audio-Service. Filter with 2.4 mm diameter, suitable for almost all in-the-ear hearing aids that work with the HF4 filter system. It is most often used with GN Resound ITE (in-the-ear) hearing aids. Earwax can reduce the performance of your hearing aid. The Cerumen Filter from Audio-Service offers reliable protection of the hearing aid from earwax contamination. One pack contains 15 HF4 cerumen filters. Blue packaging = for left side.