Guide · Weight-stack adders
8 mm vs 10 mm selector pins: measure before buying an adder
Why you should measure your machine's selector pin before buying a stack adder, why an 8 mm pin never goes in a 10 mm hole, and which adders come in which size.
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Short answer
Measure the selector pin already in your machine and buy an adder with the same diameter. Never fit an 8 mm pin into a 10 mm hole. Makers change pin sizes across models and years, so the brand name alone does not tell you the size. Stack adders are sold in 8 mm and 10 mm versions, and some come in only one.
Why the diameter matters
A stack adder slides into the same hole as the selector pin, then carries extra plates. If its stack end is thinner than the hole, it sits loose. GymPin warns against fitting an 8 mm pin into a 10 mm hole and says to match the diameter of the machine's original selector pin.[1]
How to measure your pin
GymPin tells buyers to measure their existing selector pin or stack hole before ordering, because makers may use different pin diameters across models and production years.[2] Its questions page says to use calipers on the straight shaft of the original pin.[1]
- Pull the selector pin out of the stack.
- Measure across the straight part of the shaft, not the handle, the tip or any groove.
- Read the result in millimeters. A reading near 8 mm or near 10 mm tells you which adder to order.
- If the reading is between sizes, or the pin is worn or bent, ask the machine maker before buying anything.
Brands are not a reliable guide
GymPin's FAQ article says pin sizes vary within brands, giving Matrix machines as an example that use 8 mm or 10 mm depending on year, and advises measuring the pin already in the machine.[3] Its other brand examples are GymPin's own generalization about other makers' machines, so we do not turn them into a brand-to-size chart.
We also could not read a Body Masters selector-pin bulletin, so nothing here relies on it. Your own measurement is the reliable source.
Which adders come in which size
| Adder | 8 mm | 10 mm | Notes |
|---|---|---|---|
| GymPin Original | Yes | Yes | 102 mm small end in either diameter |
| GymPin KingPin | No | Yes | 10 mm only |
| Bare Steel Stacked Weight Pin | Yes, separate product | Yes, separate product | Different stated maxima per size |
GymPin lists the Original's small end, the part that goes into the stack, as 102 mm long in 8 mm (5/16 in) or 10 mm (25/64 in) diameter.[4] The KingPin comes in 10 mm only.[1]
Bare Steel Equipment sells its 8 mm and 10 mm Stacked Weight Pins as separate products. The 10 mm version states a maximum of 135 lb, and the 8 mm version states 100 lb.[5][6] Those figures belong to each pin, not to your machine; see stack adders and machine load limits.
Picks that fit2 products
Measured 8 mm: the GymPin Original listing here is the 8 mm Raw version. Measured 10 mm: the KingPin is 10 mm only.
More on choosing
Never put the 8 mm Original into a 10 mm hole. GymPin's Original product page states 60 kg and GymPin states 60 kg for the KingPin; your machine's own limit still comes first. On Amazon, check that 'Ships from / Sold by' shows Amazon.com or GymPin.
Adder for machines with an 8 mm selector pin
Adder for machines with a 10 mm selector pin
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Questions
What size is my selector pin?
Measure it. GymPin advises measuring the straight shaft of your machine's existing selector pin with calipers, because makers use different diameters across models and production years.[2][1]
Can I use an 8 mm pin in a 10 mm hole?
No. GymPin warns against fitting an 8 mm pin into a 10 mm hole and says to match the diameter of the machine's original selector pin.[1]
Do all machines of one brand use the same pin?
Not necessarily. GymPin's FAQ article says sizes vary within brands, giving Matrix machines as an example that use 8 mm or 10 mm depending on year. That is GymPin's guidance, so measure your own pin rather than relying on the brand.[3]
Is there a published chart of pin sizes by machine brand?
We found none we could confirm. A Body Masters selector-pin bulletin could not be read, and GymPin's brand examples are its own generalization, so we do not publish a brand-to-size table.