Pillow Block Units

"H" is shaft height; "J" is the distance between bolt hole centers

Pillow blocks are designed to support a shaft: the mounting surface is on a parallel line with the axis of the shaft. Elongated bolt holes in the base, or feet, of the unit allow for some adjustment and easy mounting. NTN catalogs list the proper bolt sizes to secure the pillow block to the application.

Certain dimensions and measurements are critical to selecting the right pillow block—whether original to the equipment or as a replacement— for the application.

• Shaft diameter — The shaft diameter is matched with the appropriate corresponding bore dimensions of the bearing unit. If a properly sized unit matching the shaft is selected, the bearing will easily slide onto the shaft and into position, ready to be secured by the locking device.
• Shaft height (or backing height) — This dimension is determined by measuring the distance from the base (or bottom) of the pillow block to the center of the inner ring or shaft.
• The distance between the bolt hole centers — This measurement is taken from the center of one elongated bolt hole to the center of the housing’s other bolt hole.

The shaft size, shaft height and the distance between the bolt hole centers dimensions are listed in the appropriate NTN catalog.

Table 1 below provides a brief example of the dimensional details available. In this short catalog excerpt, the details are provided for a pillow block fitting a one-inch diameter shaft. From this you may select the proper combination of shaft height and the distance or spacing between bolt hole centers.

Examining the base

Different types of pillow block units have been cast with variations to the base of the housing. In some cases the base is a solid, flat surface; others have recessed, cut out areas along the underside of the flat base of the housing. While each design has its purpose, solid base pillow blocks such as those standard in NTN’s Ultra-Class line provide greater rigidity, dampen vibration and resist cracking when mounting bolts are overtightened.

Table 1: Pillow block housing variations—1" diameter shaft

Pillow block housing type	Insert bearing series	Shaft height (inch)	Bolt center distance (inch)	Housing material	Shaft height	Application duty
PL* P* HP UP	2 2 2 2	1 5/16 1 7/16 3 5/32 1 7/16	4 1/8 4 1/8 4 1/8 2 7/32	Cast Iron Cast Iron Cast Iron Cast Iron	Low base High base Tall base Tapped base	Normal
PP RPP	2 2	1 1/8 1 5/16	3 3/8 3 3/4	Pressed steel Pressed steel		Light
P*	2 (adapter)	1 11/16	4 3/4	Cast Iron	High base	Normal
P*	X	1 3/4	4 11/16	Cast Iron	High base	Medium
P*	3	1 49/64	5 3/16	Cast Iron	High base	Heavy

*The most commonly used cast housings are P (standard or high base) and PL (low base).