5/8 in vs 1 in rack hardware: which class your rack uses

Short answer

Two hardware classes share the same 3x3 in tube. Rogue Monster Lite, REP PR-4000 and Bells of Steel Hydra use 5/8 in parts; Rogue Monster, REP PR-5000 and Bells of Steel Manticore use 1 in parts. Find your rack's class from the maker's spec before you buy, and pick the attachment version for that class.

Picks that fitAll picks and how to choose

Synergee J-Cups, pair (2x2, 2x3 or 3x3; 5/8 in or 1 in converter)Check price on Amazon
Bells of Steel magnetic rack attachment pin, Hydra (3x3, 5/8 in holes), 5.0 in shaft, single (MAG-PIN-HDR)Check price on Amazon
Bells of Steel magnetic rack attachment pin, Manticore (3x3, 1 in holes), 5.1 in shaft, single (PIN-MAG-MTC)Check price on Amazon

Two classes on the same tube

The outside of the upright does not tell you the hardware class. A 3x3 in rack can take 5/8 in pins or 1 in pins depending on its line. That is why many makers sell the same attachment in two versions.

5/8 in works out to 15.875 mm, not 16 mm.^[1] Treat "5/8 in (16 mm)" as a rounded label.

Racks the maker lists with 5/8 in hardware

Rogue lists 5/8 in diameter laser-cut holes on the SML-2 uprights, with 5/8 in bolts, fasteners and J-cup pins.^[2]
Rogue lists the RML-690 with 3 x 3 in 11-gauge uprights and the same 5/8 in bolts and fasteners as its Infinity Series.^[3]
Rogue says its Infinity J-cup set uses a 5/8 in pin and fits only 5/8 in Infinity and R-Series units on 2 x 3 in uprights.^[4]
REP lists the PR-4000 with 3 x 3 in 11-gauge uprights and 5/8 in hardware.^[5] Its Round Sandwich J-cups for the 4000 Series use 5/8 in pins.^[6]
Bells of Steel says Hydra racks use 5/8 in holes.^[7]

Racks the maker lists with 1 in hardware

Rogue describes the RM-6 Monster Rack 2.0 as 3 x 3 in 11-gauge steel with 1 in hardware.^[8]
REP lists the PR-5000 with 3 x 3 in 11-gauge uprights and 1 in hardware.^[5]
REP says its 1000 Series standard J-cups are made for 2 x 2 in uprights with 1 in pins.^[9] So 1 in pins are not only a 3x3 thing.
Powertec says its Premium J-hooks use a 1 in peg and fit only Powertec racks with 2 3/8 in uprights.^[10]
Bells of Steel says Manticore racks use 1 in holes.^[7]

Summary table

System	Upright	Hardware class the maker lists
Rogue SML-2, RML-690 (Monster Lite)	3x3 in	5/8 in
Rogue Infinity, R-Series	2x3 in	5/8 in
Rogue Monster (RM-6)	3x3 in	1 in
REP PR-4000	3x3 in	5/8 in
REP PR-5000	3x3 in	1 in
REP PR-1000, 1050, 1100	2x2 in	1 in J-cup pins
Bells of Steel Hydra	3x3 in	5/8 in
Bells of Steel Manticore	3x3 in	1 in
Powertec	2 3/8 in	1 in peg

Same product, two pin versions

Rogue sells Ghost Roller J-Cups 2.0 in a 1 in pin version for Monster Series units and a separate 5/8 in pin version for Monster Lite units.^[11] Ordering the wrong one gets you a cup that does not fit your holes.

Synergee takes another route. Its J-cups come in 2x2, 2x3 and 3x3 versions and include a metal converter so one pair can be set up for 5/8 in or 1 in rack holes.^[12] Synergee also sells versions without the converter, so confirm the converter is in the variant or package you choose before relying on it.

Keyholes: a Bells of Steel case

A keyhole joins a larger opening to a smaller one. Bells of Steel says Manticore upright side holes combine a 1 in opening with a 5/8 in opening so 5/8 in Hydra attachments can pin in.^[7] It adds that Hydra attachments fit Manticore racks through the keyholes, though they may lift slightly when pushed upward.^[7]

That is a Bells of Steel statement about Bells of Steel parts on Bells of Steel racks. It does not mean other brands' 5/8 in parts fit other brands' 1 in racks. Never sleeve, shim or ream a hole to make a part fit.

Attachments sold by hardware class

Picks that fit3 products

Synergee: choose your upright size, then a converter version for 1 in holes or an NC version for 5/8 in holes only.

5/8 in vs 1 in rack hardware