Under ANSI B17.2 (Woodruff keys and keyseats), every key number follows a single two-part rule: the last two digits are the nominal diameter B in eighths of an inch, and the digits in front of them are the nominal width W in thirty-seconds of an inch [S2][S3][S8]. Applying that to the two part numbers in the title: key 606 = 6/32 in (3/16 in) wide × 6/8 in (3/4 in) nominal diameter, and key 808 = 8/32 in (1/4 in) wide × 8/8 in (1 in) nominal diameter [S3][S9]. Once that decoder is internalised, a print note that says "key no. 606" or "key no. 808" is unambiguous without flipping to a chart.
Woodruff keys are semi-circular disks that sit in a circular pocket milled directly into the shaft, and that geometry is what the B17.2 number describes, not the final assembled length of the key [S1][S2]. The two numbers in this article sit in the mid-range of the B17.2 stock list, the size band most commonly used on small to medium shafts for sprockets, pulleys, and pump couplings [S3][S4].
Reading the 606 and 808 Numbers Step by Step
The decoder takes the four-digit key number and slices it into two pieces [S2][S3]. For key 606, "60" is the width code and "6" is the diameter code; "60" ÷ 32 = 0.1875 in (3/16 in) wide, "6" ÷ 8 = 0.750 in (3/4 in) nominal diameter. For key 808, "80" ÷ 32 = 0.250 in (1/4 in) wide, and "8" ÷ 8 = 1.000 in (1 in) nominal diameter. Width is measured across the chord of the half-moon, the dimension that has to clear the keyway broach in the hub [S3][S4].
Several secondary suffixes modify the base code without changing the width-and-diameter pair [S3]. A "-1" suffix (for example 617-1) keeps the same width code but specifies a shorter actual length and a greater distance below shaft center, giving a less tall key for shallow keyseat applications. A decimal in the middle (such as 202.5 or 302.5) shifts the diameter by half an eighth (1/16 in) without changing the width code. These variants appear throughout the B17.2 table and are the reason machinists learn the decoder rather than memorise part numbers [S3][S5].
ASME B17.2 Stock Dimensions for #606 and #808
The ASME B17.2 stock table is the authoritative source for the tolerance band around the nominal code [S3][S4]. For key 606, the actual F length is 0.740 in, full-radius height C is 0.313 in max / 0.308 in min, flat-bottom height D is 0.303 in max / 0.297 in min, distance below shaft center E is 1/16 in, and length F tolerance is +0.000 / -0.010 in [S3]. For key 808, the actual F length is 0.992 in, full-radius height C is 0.438 in max / 0.433 in min, flat-bottom height D is 0.428 in max / 0.422 in min, and E is also 1/16 in [S3]. The wider F on the 808 (0.992 in vs 0.740 in on the 606) is the direct physical consequence of a larger diameter B [S3][S4].
The keyseat geometry that has to be cut into the shaft is also tabulated against the same key number, which is what makes B17.2 a keyseat standard as much as a key standard [S4]. For 606, the shaft keyseat width A is 0.1863-0.1880 in, depth B 0.2143 in, and seat diameter F 0.750 in (with hub keyseat 0.0937 in wide, 0.1885 in deep). For 808, shaft width A is 0.2487-0.2505 in, depth B 0.3080 in, and seat diameter F 1.000 in (with hub keyseat 0.1250 in wide, 0.2510 in deep) [S4]. Those numbers are not interchangeable: a 606 cutter will cut the wrong pocket for an 808 key, and the 1/16 in difference in E between the two sizes is small enough to look right on a caliper but is enough to change hub engagement [S3][S4].
How #606 and #808 Compare on Selection Criteria
Side by side, 606 and 808 cover the same torque band at adjacent shaft sizes, so selection is driven by shaft diameter and hub wall thickness, not by capacity [S3][S4]. Key 606 fits a 3/4 in shaft with a 0.188 in deep hub keyseat, while key 808 fits a 1 in shaft with a 0.251 in deep hub keyseat, a 33% deeper cut for one shaft-diameter step [S4]. The width-to-diameter ratio is similar (0.25 for 606, 0.25 for 808), so both behave the same way under torsion: the shaft cross-section is reduced by roughly the keyseat depth squared, and that is what the designer is really trading off [S2][S4].
For comparison against the rest of the B17.2 family, three other size pairs illustrate the same width-and-diameter rule: #404 = 4/32 in (1/8 in) wide × 4/8 in (1/2 in) diameter, #1010 = 10/32 in (5/16 in) wide × 10/8 in (1-1/4 in) diameter, and #1212 = 12/32 in (3/8 in) wide × 12/8 in (1-1/2 in) diameter [S3][S7]. Within each diameter group, the available width steps are 1/16, 3/32, 1/8, 5/32, 3/16, 7/32, 1/4, 5/16, and 3/8 in, which is why "606" and "808" both exist and neither is redundant [S3]. The 606 lives in the 3/4 in diameter group, the 808 in the 1 in diameter group; the next wider key in the 3/4 in group is 806 (1/4 in wide), and the next narrower in the 1 in group is 608 (3/16 in wide) [S3][S4].
Material, Profile Variants, and Where Woodruff Fits
Standard B17.2 Woodruff keys are usually supplied as hot-rolled or cold-drawn high-carbon steel, with stainless variants available where corrosion is a concern [S1]. The B17.2 standard covers both full-radius and flat-bottom profiles; flat-bottom keys are an ANSI-only option with no metric equivalent, and the standard leaves the choice between the two to the manufacturer, which can vary by lot even within a single part number [S2]. Hi-Pro (high-profile) keys add a lip that sits on the shaft surface to stop the key rocking in a worn seat, and that is the third profile a maintenance buyer is likely to meet on the same nominal code [S1].
The half-moon profile is the reason B17.2 keys self-align in the seat pocket, which makes them the default pick for tapered shafts, small-diameter shafts below about 5/8 in, and any application where the key can be allowed to migrate axially a few thousandths under reversing load [S3]. Parallel keys under ANSI B17.1 cover the larger shaft range and the higher-torque end, and the trade-off between the two key families is laid out in detail in ANSI B17.1 vs ISO 773: parallel key dimension standards compared. For shaft-hub geometry in the size band where 606 and 808 are used, gear and coupling selection usually flows from an AGMA Service Factor Calculation for Gearbox Selection on the driven machine, which then dictates the required key width and therefore the B17.2 number.
Limits, Failure Modes, and What B17.2 Does Not Cover
Woodruff keys are intentionally the weak link in the shaft-hub pair, and that is by design: a key costs a few cents, a gear or coupling costs orders of magnitude more, and the key shearing first protects the expensive part [S1][S2]. The trade-off is that a B17.2 key is also limited in how much torque it can carry before yielding, because the shaft cross-section is weakened by the keyseat pocket, typically by an amount proportional to the seat depth squared [S2][S4]. Reverse-load applications, where the key is asked to resist axial migration in both directions, are not the strong point of a half-moon key, and that is where a parallel key under B17.1 is usually a better fit [S2].
Outside the B17.2 scope, two practical points trip up first-time specifiers. First, the same key number can ship as either a full-radius or a flat-bottom profile, and the difference does not show up in the part description, so receiving inspection should call out which one is required for the application [S2]. Second, B17.2 covers inch dimensions only; metric Woodruff keys follow a different numbering convention and are not interchangeable with B17.2 stock, even when the nominal dimensions look similar [S1][S3]. For routine maintenance on legacy US-built machinery, sticking to the B17.2 number on the drawing remains the safest course.
Cross-References to Verify Before Ordering
Three sources are worth pulling before any 606 or 808 key is cut or ordered. The first is the ASME B17.2 stock table itself, which gives actual F length, height C, height D, and E distance below center for every number in the family [S3]. The second is the ANSI B17.2 keyseat dimension table, which lists the matching shaft keyseat width A, depth B, and seat diameter F that the cutter has to produce [S4]. The third is Machinery's Handbook, which has carried the B17.1 and B17.2 tables in the "Keys and Keyseats" chapter for decades and is the standard pocket reference on the shop floor [S5].
A reliable trackable signal for 2026 is that the B17.2 numbering convention continues to be reproduced unchanged across published references through September 2026, with no published revision of the inch Woodruff key numbering scheme [S3][S7][S9]. For a 606 application, watch for the keyseat depth B (0.2143 in) and shaft seat diameter F (0.750 in) on the shaft print; for an 808 application, the matching numbers are 0.3080 in depth and 1.000 in diameter [S4]. A second useful check is the 1/16 in E dimension, which is identical for both 606 and 808 and is the value to verify with a depth micrometer when inspecting a used shaft [S3].
For component-level specifications, see measurement test 2, and electronic test measurement 2.