Answer:
The Bilsom 303 designates the uncorded version (SLC80 22 dB, Class 4), whereas the Bilsom 304 designates the corded version (SLC80 24 dB, Class 4).
Within the Honeywell Howard Leight 300 Series foam earplug family, the Bilsom 303 refers strictly to the uncorded single-use variant, which is rated at an SLC80 of 22 dB (Class 4) for standard uncorded formats and SNR 33 dB. It is available in regular/large and small sizing profiles.
In contrast, the sibling model Bilsom 304 is the corded configuration featuring an integrated connecting cord designed to prevent loss when earplugs are removed intermittently. The corded Bilsom 304 carries an SLC80 rating of 24 dB (Class 4). Both models share the identical bullet-shaped polyurethane foam construction and EN 352-2:2002 / AS/NZS 1270:2002 regulatory approvals.
