Buying task · Weight-stack adders
Weight-stack adders
Weight stack pin adders and fractional plates: the maker's own add-ons first, then selector-pin diameter, the machine's permitted load, pin limits and clearance.
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Short answer
Start with your machine maker's own add-on weights, and only then look at a stack adder pin whose selector-pin diameter matches the pin already in your machine. Fit comes before load, and the machine's permitted load comes before both: GymPin says its pins do not certify or uprate a machine, and that the machine's permitted load takes priority.[1] An adder never lets the machine take more than its maker allows.
What stack adders are
A selectorized stack moves in fixed steps, often 10 lb or more. Two kinds of add-on fill the gaps. A fractional weight is a small plate that sits on top of the stack. A stack adder pin goes into a hole in the stack and holds plates on a sleeve. Both add weight to the stack the machine already lifts.
We do not test adders. Every size and limit here is the maker's statement for one model.
The decisions, in order
1. The machine maker's own add-ons first. Force USA's US fractional plates come as a 6 lb pair of 3 lb plates that split into 1.5 lb halves and slide onto its All-In-One Trainers' stacks.[2] Inspire lists 5 lb add-on weights as an option for the FTX.[3] REP's Altitude gallery shows drop-down add-on weights without stating amounts.[4] A maker's own part is made for that stack. See add small increments to a weight stack.
2. Selector-pin diameter. GymPin's Original has a 102 mm stack end in 8 mm (5/16 in) or 10 mm (25/64 in).[5] GymPin warns against putting an 8 mm pin into a 10 mm hole and says to match the diameter of the machine's original selector pin.[1] It also tells buyers to measure their pin first, because makers use different diameters across models and years.[6] See 8 mm vs 10 mm selector pins.
3. The machine's permitted load. GymPin says a stronger pin does not raise the machine's rating.[1] Bare Steel says to verify the cable machine's weight capacity before use.[7] If you do not know your machine's limit, find it in the maker's manual before adding anything.
4. The pin's own limit and insert length. Bare Steel states 135 lb for its 10 mm pin[7] and 100 lb for its separate 8 mm pin.[8] GymPin's Original product page states 60 kg.[6] Each limit belongs to that model and never exceeds the machine's own. The insert length must suit your stack; GymPin's is 102 mm.[5]
5. Plate clearance. Plates on an adder must clear the frame through the full movement. GymPin says to check that plates clear the full range of motion.[6]
6. Ratio. On a 2:1 machine, stack weight and what you feel at the handle differ. Inspire lists the FTX at 2:1, giving 82.5 lb per pulley from each 165 lb stack.[3] Inspire does not say what its 5 lb add-on means at the handle.[3] See 1:1 vs 2:1 cable ratio.
How to choose
- Check whether your machine's maker sells add-on or fractional weights.
- If not, measure your selector pin: 8 mm or 10 mm.
- Find the machine's permitted load in its manual.
- Pick an adder whose maker states the same pin diameter and a limit, and check plate clearance.
Two approved GymPin adders state their pin size and a limit. Choose the stack end that matches your measured pin.
Picks that fit2 products
For a machine with an 8 mm selector pin, choose the GymPin Original 2 in, 8 mm Raw. For a 10 mm pin, choose the KingPin, which GymPin makes in 10 mm only.
More on choosing
Measure the pin already in your machine first, and never use either as the selector pin. 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
Fixed add-on weights sit on top of the stack instead and need no pin, but they must fit your stack's top plate and guide rods.
Picks that fit2 products
Power Systems 61999: one 5 lb weight; the maker says it fits stacks whose guide rods are no more than 3 1/4 in apart.
More on choosing
Body-Solid: choose 2.5 lb (WSA2-5) or 5 lb (WSA5); Body-Solid names no machines, so check the plate's footprint against your stack. On Amazon, check that 'Ships from / Sold by' shows Amazon.com or the brand.
Power Systems Selectorized Machine Add-On Weight, 5 lb (61999)
Body-Solid Weight Stack Adapter Plate WSA2‑5 (2.5 lb) / WSA5 (5 lb)
Every page on weight-stack adders
Guides
- Add small increments to a weight stack: maker options first
- 8 mm vs 10 mm selector pins: measure before buying an adder
- GymPin Original vs MiniPin vs KingPin: fit and stated limits
- Stack adders and machine load limits
- 1:1 vs 2:1 cable ratio: stack weight vs what you pull
Setups with maker add-ons or a stack
- Inspire FTX Functional Trainer, Force USA All-In-One Trainers, REP Altitude cable attachment, REP Athena side-mount trainer
Key terms
Selector pin, stack adder pin, fractional weight, insert length, cable ratio, clearance and ASTM F2216.
Everything in this topic
Guides
- 1:1 vs 2:1 cable ratio: stack weight vs what you pullHelps you compare cable machines and add-on weights by the resistance at the handle, not just the stack number.
- 8 mm vs 10 mm selector pins: measure before buying an adderHelps you order a stack adder in the pin diameter your machine actually uses.
- Add small increments to a weight stack: maker options firstHelps you add a small jump in weight to your stack using the safest option your machine maker offers.
- GymPin Original vs MiniPin vs KingPin: fit and stated limitsHelps you choose the GymPin model and pin diameter that fit your machine and the plates you want to add.
- Stack adders and machine load limits: is a gym pin safe?Helps you use a stack adder inside your machine's limits and know when to stop and ask the maker.
Shortlists
- Stack adder pins with a stated pin size and limitHelps you pick a stack adder pin that matches your machine's selector-pin diameter and respects its permitted load.
Common questions
What does a 2:1 cable ratio mean?
REP explains that with a 2:1 ratio, 20 lb of stack feels like 10 lb at the handle, and the weight travels half the distance of the cable. With 1:1, 20 lb feels like 20 lb. More in 1:1 vs 2:1 cable ratio: stack weight vs what you pull
Is 2:1 worse than 1:1?
Neither is better in general. A 2:1 machine gives lighter resistance per stack plate and longer cable travel per inch of stack movement; a 1:1 machine gives the full stack at the handle. Choose by the loads and movements you need. More in 1:1 vs 2:1 cable ratio: stack weight vs what you pull
Why does my cable machine feel lighter than the stack?
It may run at 2:1. Inspire, for example, lists the FTX's two 165 lb stacks at a 2:1 ratio, giving 82.5 lb per pulley. Check your machine's listed ratio. More in 1:1 vs 2:1 cable ratio: stack weight vs what you pull
Is a 5 lb add-on 5 lb at the handle on a 2:1 machine?
Do not assume so. Inspire sells 5 lb add-ons for the 2:1 FTX but does not say whether that is stack mass or handle resistance, so ask the maker. More in 1:1 vs 2:1 cable ratio: stack weight vs what you pull
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. More in 8 mm vs 10 mm selector pins: measure before buying an adder
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. More in 8 mm vs 10 mm selector pins: measure before buying an adder
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. More in 8 mm vs 10 mm selector pins: measure before buying an adder
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. More in 8 mm vs 10 mm selector pins: measure before buying an adder
Questions
What is a stack adder pin?
A pin that goes into a hole in a weight stack and holds plates on a sleeve. GymPin's Original has a 102 mm stack end in 8 mm or 10 mm and a plate end for 2-inch Olympic plates.[5][6]
Will a GymPin fit my machine?
Only if its stack end matches your machine's selector pin. GymPin tells buyers to measure the existing pin, because diameters vary across models and years, and warns against an 8 mm pin in a 10 mm hole.[6][1]
Does an adder let me lift more than the stack?
It adds weight, but never raises what the machine may carry. GymPin says a stronger pin does not raise the machine's rating, and the machine's permitted load takes priority. See stack adders and machine load limits.[1]
What are fractional weights?
Small plates that sit on top of a stack. Force USA's US version is a pair of 3 lb plates that split into 1.5 lb halves for its All-In-One Trainers.[2]