7493 air sampling cane 6.4mm mesh PTFE screen assembly. Only available for our 25mm OD canes. Place the screen within the retaining ring, unfasten the yoke's nut & bolt, pass the now open yoke around the funnel and then tighten the nut and bolt to secure the assembly. The screen is held in place via the tension created by the springs which stretch from the yoke to the screen retaining ring.