A Conrad deep-groove ball bearing is structurally limited to about 50% of the theoretical full ball complement because the inner and outer rings are assembled concentrically, leaving no path to insert additional balls; this geometry caps load capacity by design [S2][S3].
Full-complement deep-groove bearings recover that unused space by machining a filler slot into both rings, raising the dynamic load rating by up to 45% and the static load rating by up to 45% on the same 6203 envelope, but cutting the speed ceiling from roughly 17,100 rpm (grease) to 2,000 rpm in the same lubrication regime [S1].
Why the Conrad Type Loses So Much Capacity on Paper
The Conrad assembly process requires the inner and outer races to be radially offset at one point, filled through the resulting gap, then forced concentric, which makes the cage mandatory to keep the balls distributed [S3]. Because the cage itself occupies angular space, a Conrad 6203 in the 2Z variant carries a 9,550 N dynamic and 4,800 N static load rating, while a 6203 full-complement bearing in the same 17×40×12 mm envelope reaches 14,000 N dynamic and 7,000 N static [S1].
That is not a marginal change; it is the difference between a bearing that survives a radial gearbox load and one that survives a heavy conveyor idler shock event on the same shaft diameter. Deep-groove ball bearings already have higher load ratings for their size than shallow-groove variants, but lower ratings for their size than most roller bearings, so the complement question is the single biggest capacity lever still available inside the deep-groove family [S3].
How Full-Complement Designs Recover the Lost Balls
Two construction paths exist. The first, the filler-notch (or slot-fill) design, grinds a small dam on the inner and outer rings so a press-fit ball set can be snapped over the entry point after the standard complement is installed; the dam is sized so that interference is maintained even at the smallest ball and maximum radial play [S2][S3].
The second path, used in angular-contact full-complement X205 type bearings, simply exploits the fact that an angular-contact raceway already includes a dam, then thermally expands the outer ring during assembly to drop the extra balls in before cooling locks them in place [S2]. Both routes trade one performance dimension for another: the filler-notch geometry is radial-load dominant and weak in axial loading because the notch itself interferes with ball rotation under thrust, while the X205 angular-contact version is built for high thrust and accepts reduced radial capacity where the contact ellipse intersects the dam [S2][S4].
The Speed, Friction, and Lubrication Penalty
Full-complement ball bearings are deliberately slowed by their own ball-to-ball contact. With the cage removed, the inner ring acts as a sun gear, driving every ball in the same direction, and at each contact point the surfaces are moving in opposing directions, so sliding friction dominates the torque budget [S2]. In cylindrical-roller form, the same trade shows up as a 15% capacity gain bought at a 50% speed-derating, from 3,200 rpm down to 1,600 rpm under oil lubrication for a 100×215×73 mm FAG envelope [S5].
The 6203 example mirrors that pattern in ball form: 17,100 rpm with grease and 20,100 rpm with oil for the caged version, versus 2,000 rpm and 3,000 rpm respectively for the full-complement variant, a roughly 8× to 7× reduction in allowable speed on the same bore [S1]. Ceramic balls partially offset this by lowering wear and friction in full-complement X205 service, but do not eliminate the speed penalty [S2].
Decision Matrix: Conrad vs Full-Complement on Four Criteria
On radial load capacity, full-complement wins by up to 45% on dynamic and 45% on static rating in matched 6203 comparisons [S1]. On axial load capacity, Conrad wins decisively; heavy 6200/6300 series take axial loads up to 50% of the static radial rating, and full-complement bearings are not recommended for axial loads at all because the filling slot interferes with ball rotation under thrust [S4].
On speed, Conrad wins by roughly a factor of 7–8× on the same lubrication and bore, and is the only choice above roughly 3,000 rpm in 6203-class sizes [S1]. On tolerance to misalignment, Conrad again wins; the slot-fill notches that enable full-complement assembly mechanically weaken both rings and reduce the misalignment budget the bearing can absorb [S3]. A simplified mapping: specify Conrad for combined radial + axial loads above roughly 3,000 rpm, specify full-complement for heavy pure-radial, low-speed, heavily shock-loaded service such as conveyor idlers, crane sheaves, and slow industrial gearboxes.
Minimum-Load and Lubrication Constraints
For long life, the actual applied load should sit between 6% and 12% of the bearing's dynamic load rating, a rule that holds across caged and full-complement deep-groove designs and is enforced because underloading promotes skidding and smearing [S4]. Schaeffler's published minimum-load guidance goes further: for full-complement or caged toroidal roller bearings, the minimum radial load is P > C₀/75, a stricter floor than for many other rolling-element types [S8].
Stainless-steel variants shift the entire rating band downward: AISI 440C / KS440 stainless carries about 80–85% of a chrome-steel dynamic rating and 75–80% of its static rating, a drop that applies identically to caged and full-complement builds, so a 14,000 N dynamic 6203 in chrome shrinks to roughly 11,200–11,900 N in the same envelope in stainless [S4]. When high load capacity is the entire reason for picking full-complement, dropping the ball material to stainless can erase the very gain that justified the choice.
Where the Trade Is Worth It and Where It Is Not
Specify full-complement deep-groove ball bearings when the duty cycle is heavy radial load at low speed, the duty is shock-loaded rather than continuous, the lubricant is grease rather than oil, and any axial load is small and unidirectional so the filler-notch orientation can be aligned with it [S2][S4]. Specify Conrad (caged) deep-groove ball bearings when the application combines radial and axial load, runs above roughly 3,000 rpm in 6203-class sizes, requires accurate axial location, or demands the longest possible L10 life under steady duty [S1][S3].
For an engineering procurement map, this lines up with bearing material decisions covered in the chrome steel vs silicon nitride bearing balls selection guide, because full-complement X205 builds are the canonical place where Si3N4 ceramic balls are specified to recover friction lost to ball-to-ball sliding [S2]. A simple working rule: if speed × radial load points you into the full-complement quadrant, plan to derate speed by an order of magnitude and re-check the L10 life at the new operating point before signing the drawing.
Trackable signals for the next design review: (a) whether your application's actual applied load sits inside the 6–12% of C dynamic band once the full-complement gain is applied, and (b) whether the speed-derated thermal balance at the new rpm limit still allows the chosen grease to hold its base-oil viscosity at operating temperature, since full-complement ball-to-ball friction is the dominant heat source in this geometry [S2][S4].
The underlying component specifications are covered under ball bearing, dry type transformer, and electronic load.