2 inch <> 3 inch duct adapter (50 mm <> 75 mm)

Every permutation for every use case!

Quick thank you for all the positive comments for the 3 inch to 4 inch adapter that I previously created, so I thought I would do the same extensive modeling to create a 2 inch to 3 inch adapter. I hope you find this useful, too - and please let me know if you have any requests!

Why I made this

This is designed to bring two ducts or vents of 2 inches (~50mm) and 3 inches (~75mm) together.

I've taken a lot of care to make sure the fluid flow inside is smooth as there are no sharp edges inside. Many of the cheap Amazon / Temu ducts you find are simple stacked cylinders where there is an abrupt sharp corner where the two cylinders meet. This causes fluid friction and slows down your cooling, heating, trap debris, or whatever. Whatever you are using this for, I presume you don't like unnecessary turbulence for no reason.

Okay, but why is there more than one adapter?

I've made different versions to cover different use cases and the inevitable differences between actual measurements versus nominal 2 and 3 inches measurements. This is how I organized them.

• OD: nominal outer diameter without any variance
  • OD2 = 2 inches outer diameter, exactly as nominal
  • OD3 = 3 inches outer diameter, exactly as nominal
• Male: nominal outer diameter + variance
  • M2 = 2 inches, plus variance
  • M3 = 3 inches, plus variance
• Female: nominal outer diameter - variance
  • F2 = 2 inches, minus variance
  • F3 = 3 inches, minus variance

I've put them on three different plates.

Remember to de-select what you don't need, otherwise you get all nine possible permutations.

Scroll to the bottom for detailed measurements in both imperial and metric, otherwise more detailed help below.

Ok…so many options. Where do I start?

1. Measure your existing item that you're connecting to. Get both outer and inner diameter. Use a caliper if you can. 
2. Choose whether you want the printed adapter to fit OVER or fit UNDER that existing item.
3. Choose the right adapter based on the table below, with the closest fit for inner or outer diameter 
   1. Note: if your hose outer diameter is larger than the inner of the male option, then you must choose to fit UNDER
   2. Note: if your hose is inner diameter is smaller than the outer of the female option, then you must choose to fit OVER

I'm still confused. Got examples on how to select the right adapter?

Yes, let's go through some examples!

Example #1:

• Say you measure your hose. It's exactly 3" or 76mm outer diameter, and 2.9" on the inside. Great! You've got a couple choices.
• You can either:
  • Choose one of the male 3 (M3) options because the inner diameter is 3" (76mm) so it fits OVER your existing hose
  • Choose one of the female 3 (F3) options because the outer diameter is 2.88" (73mm) so it fits UNDER your hose. But I might use a clamp because it's 0.02" (6mm) too small / loose.
• You cannot use any of the OD3 options because it is the same size as what I'm connecting to.
• You may also want to consider which direction the air / debris / fluid is flowing

Example #2:

• You measure your duct and it's 3.2" (81mm) outer diameter, and inner diameter is 3.00" or 76.20mm 
• You would choose an OD3 adapter because the outer diameter is 3" (76.2mm) and the printed adapter fits UNDER the duct.
• It may not even need a clamp because it's a tight tolerance.

Options available and detailed measurements (US imperial)

Options available and detailed measurements (Metric)