Stacking Ball Stretcher V2

Stacker V2 🍒⬇

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Stacker V2 is a complete, from-scratch redesign of the stackable ball stretcher concept originally created by KDxGP's STRECHR. The original STRECHR is a great design and the one that started me down this rabbit hole (phrasing), but after months of daily use I had a long list of "I wish this did..." moments. So I sat down, learned OpenSCAD, over-engineered the absolute hell out of it, and here we are.

⚠ V2 is NOT compatible with V1. Don't try it. They will not interlock. Think of it like an ex — you've moved on to better things.

What's New in V2 (aka "Why Your V1 is Now a Paperweight")

🔒 Anti-Twist Interlocking System

V1's rings could twist freely once stacked. Cute for a fidget spinner, less cute when you're walking around and your stack decides to slowly unscrew itself like a jar of pickles. V2 uses a four-position indexed joint with tongue keys and matching pockets. Rings lock at 0°, 90°, 180°, or 270° and stay put. Twist between positions? Nope — solid material blocks you. Your stack is now as committed as you are.

🛡 Anti-Pinch Protected Seams

Each ring is printed as two semicircular halves (so it can actually go on). In V1, the seam between halves could leave a skin-facing gap. If you've experienced The Pinch™, you know exactly what I'm talking about, and you just winced. V2's seams use a 2mm inner shield with a hidden pocket on the mating face. The gap is buried behind solid material. Clearance is radial, not skin-facing. Your boys are safe.

📐 Lower Profile Ridges

The V1 tongue-and-groove joint stuck up pretty high, which meant you needed a decent angle to slide the next ring over. More angle = more wrestling = more "is this even worth it?" moments. V2's joint profile is lower and chamfered with a 0.8mm lead-in, so the next ring slides on with significantly less effort. As a bonus, the lower ridges mean each ring is slightly heavier — more mass pulling where you want it. Physics is on your side.

🔄 Smooth Transition Rings (NEW)

This is the big one. V1 only came in fixed sizes — if you started with 39mm, everything was 39mm, forever. V2 introduces transition rings that smoothly flare from one size to the next. Available in one-step (3mm) and two-step (6mm) jumps. I personally run a stack that starts at 39mm and transitions to 45mm. This lets you accommodate more skin as you go up the stack, which means taller stacks are actually comfortable instead of feeling like your sack is being interrogated.

👑 Comfort Top Cap (NEW)

The terminal ring on your stack now has a rounded bullnose edge on top — a 5mm radius outer rollover plus a 2.5mm inner roundover. No more sharp PLA edges digging into you. The comfort top is a receiving-only piece (no upper joint), so your stack ends with a smooth, pressure-distributing crown. Your skin will thank you.

⚖ Heavier Rings

The redesigned lower-profile joints actually leave more solid material in each ring. More plastic = more weight = more stretch. This wasn't even intentional — it's just a happy side effect of better engineering. Sometimes the universe rewards good design decisions.

Available Sizes

Each piece is published as a single 180° half. Print two copies of each half and rotate the second one 180° during assembly. Sizes are by inner diameter (the actual opening):

The right diameter is determined by your anatomy, not your experience level. Everyone's body is different — measure first, then print.

Finding Your Size

You need to measure the circumference of your scrotum and convert it to a diameter. Here's how:

1. Measure when relaxed. Take your measurement after a warm shower or bath when your scrotum is hanging naturally. Being cold and tight will give you a too-small number.

2. Wrap a flexible tape or string around your scrotum at the point just below the base of the penis and above the top of the testicles — right where the ring will sit.

3. Pull snug, not tight. The tape should be secure enough that your testicles can't slip through, but not so tight that it digs in or restricts blood flow. Think "firm handshake," not "tourniquet."

4. Record the circumference. If you used string, mark where it overlaps and measure the length against a ruler.

5. Repeat 4–5 times at different times of day and average the results. Discard any obvious outliers. Your body changes size throughout the day — averaging gives you the real number.

6. Divide by π (3.14) to get your diameter. For example: 120mm circumference ÷ 3.14 = ~38mm diameter → you'd start with the 39mm size.

Round to the nearest available size. When in between sizes, round up — too tight is uncomfortable and potentially unsafe, too loose just means it might slide. You can always go down a size later.

⚠ Safety note: A properly sized stretcher should be snug but never painful. If you feel pain, numbness, or notice any discoloration, remove it immediately. Seriously — don't be a hero.

Piece Types

🚀 Beginner Progression

New to stacking? Here's how most people work their way up.

Stage 1: Base + Top

Start with just two pieces — a base ring and a comfort top in your measured size. Wear this until it feels like nothing. Get used to how it sits, how it feels during the day, and how your body responds. This is your baseline.

Stage 2: First Extension

Once you're comfortable (give it at least a week or two), add a single straight extension between the base and top. You now have a three-piece stack. This is where most people notice the stretch starting to happen.

Stage 3: Second Extension

Ready for more height? You have options:

• Go gradual with a 1.25x or 1.5x height extension instead of a full 1x ring. These shorter extensions let you add height in smaller steps — less of a jump, more of a ramp.

• Go full send and add another standard 1x straight extension. If Stage 2 felt easy, this is the move.

Stage 4: Transitions for Taller Stacks

As your stack gets taller, you'll notice the skin higher up the stack can feel tighter — there's simply more skin being gathered as you go up. This is where transition rings earn their keep. A transition flares from your base diameter to a larger one (e.g., 39mm → 42mm or 39mm → 45mm), giving the upper portion of the stack more room to accommodate the extra skin. If your stack is 4+ rings and the top feels snug, it's time to introduce a transition.

The Short Version

My Reference Stack (The "Daily Driver")

From bottom to top:

1. 🔴 39mm Base (with retention lip)

2. ⚫ 39mm Straight Extension

3. ⚫ 39mm Straight Extension

4. 🔵 39mm → 45mm Transition (the smooth flare)

5. ⚫ 45mm Straight Extension

6. ⚫ 45mm Straight Extension

7. 👑 45mm Comfort Top

Total height: 106mm. Seven layers, fourteen printed halves, five unique geometries. Alternate each layer's seam by 90° for maximum stability.

🖨 Print Settings

Tips

• Sand the inner surfaces lightly after printing for maximum comfort. 400-grit works great.

• Print in pairs — you need two of each half. Batch them on the same plate.

• Check your fit with a single straight ring first before committing to a full stack. If it's too tight, go up one size. If it falls off, go down. This is not the place for wishful thinking.

• All joint faces are designed at ≤45° slopes, so there's truly zero need for supports. If your slicer insists, tell it to mind its own business.

🔮 Coming Soon: Weighted Extension

For those who want serious pull, there's a weighted bearing cartridge in development. It replaces two straight rings with a two-piece shell (tray + lid) that holds 15mm steel bearing balls in a circular race. Up to 12 balls per cartridge depending on ring size. It uses the same indexed joints as the rest of the V2 system. Stay tuned.

Credits & License

This is a remix of KDxGP's STRECHR — the original stackable ball stretcher that started it all. Full credit to KDxGP for the brilliant core concept. V2 is a ground-up parametric redesign in OpenSCAD, but the DNA is STRECHR's.

License: CC BY-NC-SA 4.0

• ✅ Share and remix with attribution

• ❌ No commercial use

• 🔄 Share-alike required