How to distinguish slewing ring ball plug, grease hole and dowel pin hole. Watch our short video to learn their positions, functions and key installation notes for slewing bearings.
Slewing Ring Ball Plug, Grease Hole and Dowel Pin: How to Identify Positions & Functions
Many customers get confused about three critical holes on slewing rings during inspection and installation: ball plug, grease hole, and dowel pin hole. Misidentification may trigger assembly faults, insufficient lubrication and shortened service life of slewing bearings.
We made a 24-second demonstration video to visually display these three structures and their standard positions on the slewing ring.
1. Ball Plug (Filling Plug)
The position pointed out in the video is the ball plug, also called filling plug.
– Function: The hole is reserved for loading steel balls into the raceway during manufacturing. After steel ball assembly, the ball plug seals the ball filling hole.
– ⚠️ Important Warning: Do not remove the ball plug arbitrarily after delivery. Taking out the plug will lead to steel ball loss and permanent damage to the slewing ring.
– Do NOT inject grease through the ball plug.
2. Grease Hole (Lubrication Hole)
The grease hole is the dedicated passage for maintenance lubrication.
– Function: Fit with a grease nipple to feed lubricating grease into the rolling raceway periodically.
– Maintenance Tip: Regular greasing must be operated via grease holes to minimize friction and rolling element abrasion.
3. Dowel Pin & Dowel Pin Hole
The small circular hole near the ball plug is the dowel pin hole, matched with the dowel pin.
– Function: The dowel pin acts as a positioning part. It locks the relative position between inner ring and outer ring during production, transportation and assembly, avoiding accidental rotation offset.
– Note: Do not knock out the dowel pin without technical guidance.
Typical Common Errors
1. Mix up ball plug, grease hole and dowel pin hole; try to add grease through ball plug or pin hole.
2. Randomly dismantle ball plugs or dowel pins on-site.
3. Ignore component position marks when installing slewing bearings on machinery.
Professional Suggestions
Before mounting your slewing ring, verify the locations of ball plug, grease hole and dowel pin against technical drawings, product pictures and our demonstration video. Contact our technical team anytime if you have trouble distinguishing these structures.
We provide custom slewing bearings for tower cranes, mining machines, excavators, port machinery and rotary equipment. Each product is fully inspected, with clear marking of soft zone, ball plug, grease hole and dowel pin positions to satisfy global clients.