FafnirRCJ-2-15/16Four-Bolt Square Flange Mount Bearing Unit, 2-15/16″ Bore, Eccentric Locking Collar, Cast Iron, Non-Expansion

Product Description

What this part is

A complete four-bolt square flange mounted bearing unit — cast iron housing, wide-inner-ring insert and eccentric locking collar supplied together as an assembly. Timken’s official name for it is Fafnir Four-Bolt Flanged Mounted Bearing, Eccentric Locking Collar, industrial series. The insert inside is bearing designation G1215KRRB, which is available on its own if the housing outlives the bearing. The 2-15/16 in bore is a large mounted-bearing size, and at that diameter the four-bolt square flange exists specifically to spread the mounting load across four fasteners instead of two.

Decoding the designation

Fafnir’s mounted-unit codes read left to right as housing series, locking method, housing style. R is the Regular, industrial-duty housing series; in the Fafnir housing letters, T is the light or thin series and L is light, so R sits at the heavy end of the range. C is Collar-lock, meaning the unit locks with an eccentric collar rather than setscrews. J is the four-bolt square flange housing style. Put together, RCJ2-15/16 is a regular-duty four-bolt square flange unit with an eccentric locking collar for a 2-15/16 in shaft. Nearby variants are worth knowing so you do not order the wrong housing: RCJT is the two-bolt flange, RCJO is a four-bolt unit with a different flange outline, RCJC is the concentric-collar version, and TCJ is the same four-bolt style in the light housing series.

Why the eccentric collar matters

This is the single most important thing to understand about the part. It is not a setscrew unit. The insert’s extended inner ring has an eccentric cam face at one end, and the collar has a matching eccentric bore. You slide the whole unit onto a plain straight shaft, then rotate the collar in the direction of shaft rotation until the two eccentrics jam against one another; the collar’s setscrew then locks the collar to the shaft. What you get is a grip distributed over a wide contact arc rather than two point loads from setscrew tips, which is why eccentric-collar units hold noticeably better under reversing loads, shock and continuous vibration — conditions where setscrews back out.

The trade-off is that an eccentric collar is DIRECTIONAL. Fit it so that the collar tightens in the direction the shaft turns. If you install it backwards, normal rotation works to unwind the collar and it will loosen in service, usually taking the shaft finish with it. If the shaft reverses, or if you are in any doubt, mark the rotation direction on the guard before you assemble and check the collar orientation against it. Get this one detail right and the unit will hold; get it wrong and no amount of setscrew torque saves you.

What these specs mean in practice

The unit uses a shroud seal arrangement (contact seals per Applied’s listing) and is factory pre-lubricated with a grease fitting for relube, so it is a serviceable unit rather than a sealed-for-life throwaway — important at this size, where replacement is expensive and a grease schedule is cheap. It is a non-expansion unit, meaning it locates the shaft axially. On a shaft carried by two units, one should hold position and the other should permit axial movement so thermal growth is not fought by the bearings; a 2-15/16 in shaft is typically long enough that growth is a real number, not a rounding error.

Load capacity is 15,500 lbf dynamic and 10,100 lbf static. The static rating is the one that governs on equipment that sits loaded, gets shock-loaded while stopped, or indexes rather than runs continuously; the dynamic rating is what feeds an L10 life calculation for continuous rotation. At this bore size you are typically in heavy conveying, crushing-adjacent, agricultural or bulk-handling service where both numbers matter.

Published ratings and mounting data

Bore: 2-15/16 in
Insert bearing: G1215KRRB (available separately)
Dynamic load rating C: 68,900 N / 15,500 lbf
Static load rating C₀: 44,800 N / 10,100 lbf
Total length L: 196.8 mm / 7.748 in
Housing width A: 66.7 mm / 2.626 in
Flange thickness A1: 22.2 mm / 0.874 in
Bearing center from housing end A2: 41.9 mm / 1.65 in
Bolt hole spacing: 152.4 mm / 6.000 in
Bolt hole size N: 16 mm / 0.63 in, for M16 bolts
B1: 92.1 mm / 3.626 in
S1: 54.8 mm / 2.157 in
D: 161.9 mm / 6.374 in
E: 96.7 mm / 3.807 in
d1: 101.6 mm / 4.000 in
Housing: cast iron, four-bolt square flange
Locking: eccentric locking collar
Seal: shroud seal, contact type
Lubrication: factory pre-lubricated, grease fitting for relubrication
Expansion: non-expansion

Maximum speed is not published for this size. Timken’s CAD record carries a limiting speed only for the smaller sizes in this series, and no figure is given for RCJ2-15/16, so none is stated here rather than borrowing a number from an adjacent size. If speed is a governing constraint on your application, contact Timken with the application details for a rating.

The two dimensions that decide a retrofit are the 6.000 in bolt hole spacing and the 3.626 in B1 figure, which together fix where the shaft centerline lands relative to the mounting face. Also confirm the M16 clearance holes, since inch-series frames drilled for 5/8 in bolts are close but not identical.

Quantity and configuration

Three units are in stock, which at this bore size is a useful position — enough for both ends of a shaft plus a spare on the shelf, and enough that you are not hunting a second unit after the first one goes in. All three are from the same holding. Order the quantity you need and ask about pricing if you are taking all three.

Fitting notes

Determine shaft rotation direction first and orient the eccentric collar so it tightens with rotation — this is not optional. Slide the unit onto a clean, deburred shaft; do not hammer it, since blows transmitted through the inner ring damage the ball path. Mount the housing flat against a clean, flat surface and bring the four M16 bolts up in a cross pattern, in stages, so the cast housing is not distorted. Then set the collar: rotate it hard by hand or with a drift in the direction of rotation until the eccentrics lock, and only then tighten the collar setscrew. Give the unit its first relube on schedule rather than assuming the factory charge is enough for the life of the bearing, and re-check the collar after initial run-in.

Interchange guidance

Fafnir is a Timken brand and this remains an active Timken catalog number, so current documentation is available. Timken lists it as RCJ2 15/16, with alternate rendering RCJ215/16 and SAP Material ID 100200624; distributor systems also carry RCJ-2-15/16 and RCJ2-15/16, so search all of those spellings. The insert alone crosses as G1215KRRB. When considering a substitution, do not assume the housing styles interchange — RCJT (two-bolt) and RCJO (different four-bolt flange) share the bore but not the mounting, and RCJC swaps the eccentric collar for a concentric one, which changes the installation procedure and the holding behavior described above.