Some of those companies that may soon be buyable include Donaldson, a filter manufacturer, and Ethan Allen.

While these are not technically filters but accessory lenses, they are sold by filter manufacturers as part of their product lines, using the same holders and attachment systems.

Some of the fears associated with Internet filtering in schools include: the risk of supporting a predominant ideology, that views held by filter manufacturers are being imposed on students, over blocking of useful information, and under blocking of harmful information.

Regulators are investigating whether the chemical fluid, which Baxter began using in December, is used by other filter manufacturers and whether other patients might have been affected.

But here he was, beyond his wildest dreams, a 66-year-old former sales manager for a filter manufacturer, his suit traded in for a kelly green uniform, spending his afternoon and evening in a stainless-steel room smaller than some of the cars that whizzed by the parkway's busiest toll plaza.

At the Water Quality Association, an association of filter manufacturers, Keith Reid, a spokesman, said some filters have pores smaller than bacteria.

Change or clean filter media as recommended by the filter manufacturers.

He developed a set of graduated neutral density filters and had them produced by Singh-Ray, a filter manufacturer.

Most filter manufacturers make kits with easy-to-follow illustrated instruction sheets for amateurs.

Her father, who is retired, was the president and chief executive officer of Purolator Inc., the filter manufacturer and armored-truck company.