Proposal to establish sampling plane diameter of 300 mm or 12" with wall thickness of up to 1.5 mm, specify sampling tunnel straight section length between 8D and 10D, require single sampling plane layout with two PN probes on top and two PM probes on bottom, allow 4-probe sampling plane with flow splitter for PN connections only, prohibit flow splitter use for PM connection, permit sampling tunnel attachment directly to enclosure outlet or to 90-degree bend after enclosure, and standardize disc brake adapter and fixture and reduce drum brake S-cam length.