SKF71904ACXP4ADGAAngular Contact Ball Bearing – 20 mm ID, 37 mm OD, 9 mm Width, Open, 25°, Extra-Light Preload, Universal Matched Pair

Product Description

What this part is

SKF 71904-ACX/P4ADGA super-precision angular contact ball bearing, supplied as a universally matched pair. Bore 20 mm, outside diameter 37 mm, width 9 mm per bearing, 18 mm across the pair. ISO size 71904, also written 7904.

Decoding the designation

71904 is the ISO 19 dimension series at a 20 mm bore. AC is the SKF code for a 25° contact angle. P4A is the super-precision tolerance and running-accuracy class, equivalent to ABEC 7 with SKF’s own running-accuracy limits. DGA is a set of two matched for universal arrangement at extra-light preload, SKF preload class A.

What these specs mean in practice

The 25° contact angle gives high axial stiffness and thrust capacity for the envelope, and the 19 series keeps the cross-section slim for compact spindle heads. Extra-light preload holds friction and heat generation to a minimum, which is what allows the 75,000 rpm limiting speed. The phenolic cage is light and tolerant of oil-air and oil-mist lubrication. Dynamic capacity is 5.72 kN and static capacity 3.05 kN per bearing, over an operating range of –30 to 110 °C.

Quantity and configuration

Two bearings, matched as a set. Universal grinding allows back-to-back, face-to-face or tandem arrangement, with preload established as the ground ring faces are clamped together. Each bearing carries 15 chrome steel balls of 4.762 mm diameter and weighs 0.035 kg.

Preload and clearance

Extra-light preload, ground into the ring faces. A preloaded matched pair has no operating radial internal clearance, so clearance classes such as CN do not apply.

Fitting notes

The outer rings carry a mark across the outside diameter; the marks are aligned to hold the intended arrangement. Shaft and housing seats are held to matching precision tolerances, and both bearings are clamped as one unit against a common shoulder.

Interchange guidance

SKF 71904 ACDGA/P4A is the current SKF designation for this execution and specification. SKF 71904 ACDGA/HCP4A is the same size, angle and preload with silicon nitride balls, a hybrid variant. SKF 71904 ACDGB/P4A shares the size and angle but is supplied as a fixed back-to-back pair, so it is a related arrangement. SKF 71904 CD/P4ADGA is the same envelope at a 15° contact angle, a related size.