Unlike the bearings NHI's "A" and "H" Series idler pulleys, New Hampshire Industries "O" Series of idler pulleys use bearings without rolling elements to lower the friction when turned.  They instead use what is curiously called a "plane" bearing, derived from using a lubricant between two flat planes to lower the friction and thus allow relative motion between them.  In the case of idler pulleys, you just have to envision that these planes are wrapped into cylinders, thus allowing rotary motion about an axis.  Rotary plane bearings are also referred to as "bushings".

Designed for high load, low speed idler applications, plane bearings are today built at varying levels of sophistication.  At the low end are the porous cast bronzes, powder metal bronzes, and powder metal steel bushings.  Oil fills the pores in these parts as the friction reducer, coming to the surface when the part is loaded and friction occurs.  More recently, some bushing manufacturers have started to employ sacrificial materials bonded to a tougher housing (like PTFE bonded to a steel shell) to increase load carrying capacity for a given size of bushing.

New Hampshire Industries has used bushings since early in the company's history, starting with the porous bushings.  Today NHI still uses porous bushings as well as the lined bushings where the application calls for higher performance.  The choice is a matter of cost-effectiveness, not using the higher priced lined bushing when a cast bronze or powder metal steel will do.

NHI "O" Series idler pulleys are manufactured by one of three methods:

• Stamped parts, with the same sizing as our "A" Series idlers, with either a single (Ø5/8"ID) powder steel bushing, or a double (adds a second bushing with a Ø3/8" ID) powder steel bushing set;
• Utilizing split-formed pulleys and their hubs with either bronze bushings or lined bushings; and
• Fully machined products, also using either bronze or lined bushings.

With the exception of the stock "O" series stamped parts, this product line is usually Made-To-Order (MTO), designed to fit a specific application.  Call NHI at (800) 654-1090 with your requirements - we can take our vast array of standard components to create the custom design that you need if we can't find an existing product to fit your application.