Guide · Measuring and buying
2x2 vs 50 mm, 3x3 vs 75 mm and 60 mm rack tubing
Imperial and metric rack tubes are different sizes. The exact numbers, how makers label 60 mm tubing, and why the label alone never proves fit.
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Short answer
They are different sizes. A 2x2 in upright is 50.8 mm, not 50 mm, and a 3x3 in upright is 76.2 mm, 1.2 mm per side larger than 75 mm. Metric 60 mm tubing is sold as "2.3 in" by one maker and "2.4 in" by another. A label never proves fit; measure your rack and match the attachment maker's stated size or host list.
The numbers
One inch is defined as exactly 25.4 mm.[1] Everything in this table is calculated from that definition. None of it is a measurement of any rack, and none of it is a fit tolerance.
| Nominal label | Exact calculated size | Near-miss size | Difference |
|---|---|---|---|
| 2 x 2 in | 50.8 x 50.8 mm | 50 x 50 mm | 0.8 mm per side[1] |
| 3 x 3 in | 76.2 x 76.2 mm | 75 x 75 mm | 1.2 mm per side[1] |
| 60 x 60 mm | about 2.362 in | labeled 2.3 in or 2.4 in | a rounding choice[1] |
| 2 3/8 in | 60.325 mm (calculated) | 60 mm | not the same label |
Those gaps look small. No maker we found publishes how much clearance its parts allow, so there is no basis for calling a near-miss size "close enough". The difference is not something to judge by eye.
How makers label 60 mm tubing
Bells of Steel says every one of its racks uses either 2.3 x 2.3 in (60 x 60 mm) or 3 x 3 in (76.2 x 76.2 mm) square tubing.[2] Force USA lists MyRack uprights as 2.4 in square (60 mm).[3] Both describe 60 mm tubing. If you only read the inch label, the two look like different sizes; if you only read "60 mm", you might assume both makers' attachments interchange. Neither shortcut is safe.
Powertec uses a third size. It says its Premium J-hooks fit only Powertec power racks and half racks with 2 3/8 x 2 3/8 in uprights.[4]
75 mm racks
REP's ISO arm FAQ, an undated maker PDF, says the arms fit 75 x 75 mm REP racks.[5] REP's rack guide labels its PR-4000 and PR-5000 uprights 3 x 3 in.[6] We report both as REP states them and do not merge them; ask REP which applies to your rack's generation.
What Bells of Steel says about other brands' 3x3 racks
Bells of Steel says the Hydra version of its standard J-cups fits Hydra racks and non-Bells of Steel racks with true 3 x 3 in uprights and 5/8 in holes.[7] That statement has two conditions, and both must hold. It is not a list of approved brands, and it does not cover 75 mm racks or 1 in holes.
What to do
- Measure your uprights across both pairs of faces. Our measuring guide shows how.
- Compare your number with the maker's published size for your rack model.
- Read the attachment maker's stated upright size, hole size and host list.
- If your rack is not on the list and the sizes do not match exactly, ask the attachment maker before you buy.
Attachments sold by stated upright size
These approved J-cups each state the upright size they are made for. Pick the class that matches your measurement.
3x3 in uprights
Picks that fit2 products
Synergee: choose a 3x3 in variant (converter version for 1 in holes, NC version for 5/8 in holes only).
More on choosing
Fringe Sport: the 3x3 pair is for 1 in holes. On Amazon, check that Ships from / Sold by is Amazon.com or the brand.
Choose Synergee if your rack is not on any maker's named list
Synergee J-Cups, pair (2x2, 2x3 or 3x3; 5/8 in or 1 in converter)
Fringe Sport J-Cups 3x3 pair, 1 in holes (JCUP‑FS‑3x3‑Black)
2x3 in uprights
Picks that fit3 products
Titan T-3 J-Hooks are for Titan T-3 racks only. Fringe Sport's 2x3 pair is for 2x3 in racks that take 5/8 in hardware.
More on choosing
Synergee: choose a 2x3 in variant. On Amazon, check that Ships from / Sold by is Amazon.com or the brand.
Choose the Titan T-3 J-Hooks for a Titan T-3 rack
2x3 J-cups for racks with 5/8 in hardware
Choose Synergee if your rack is not on any maker's named list
Synergee J-Cups, pair (2x2, 2x3 or 3x3; 5/8 in or 1 in converter)
2x2 in uprights
Picks that fit2 products
Synergee: choose the 2x2 in converter variant. Sunny SF-XFA007: only for the Sunny Powerzone models Sunny lists.
More on choosing
On Amazon, check that Ships from / Sold by is Amazon.com or the brand.
Choose Synergee if your rack is not on any maker's named list
Synergee J-Cups, pair (2x2, 2x3 or 3x3; 5/8 in or 1 in converter)
Choose the Sunny SF-XFA007 for a listed Sunny Powerzone cage
Sunny Health & Fitness J-Hooks barbell holder, 2‑piece set (SF‑XFA007)
No approved attachment in our catalog states 60 mm or 75 mm uprights yet.
Next
Questions
Will 75 mm J-cups fit my 3x3 rack?
Not on the strength of the label. 3x3 in works out to 76.2 mm, 1.2 mm per side larger than 75 mm. Only the attachment maker's host list or stated upright size can answer it.[1]
Is 60 mm the same as 2.4 in?
60 mm is about 2.362 in. Force USA labels its 60 mm MyRack tubing 2.4 in, while Bells of Steel labels its 60 mm tubing 2.3 in. Both are rounded labels for the same metric size.[1][3][2]
Is 2x2 the same as 50 mm?
No. A 2x2 in upright works out to 50.8 x 50.8 mm, which is not the same size as a 50 x 50 mm metric tube.[1]
Do Bells of Steel J-cups fit other brands' 3x3 racks?
Bells of Steel says the Hydra version of its standard J-cups fits non-Bells of Steel racks with true 3 x 3 in uprights and 5/8 in holes. Both conditions apply; measure before relying on it.[7]