Favorite flat mount dropouts?

We’re currently testing a 3D-printed FM160 “adapter”. It’s roughly $40-50. A FM140 adapter would be ~$5 cheaper. FM160 allows you to rotate the caliper to give more caliper-SS clearance. Not much cheaper than the other options, but much faster and more accurate IMO.


That’s definitely the most elegant solution! I’d love to hear the results of your testing.

The fabrication of it was very easy but did require some care when setting everything in the sub assembly fixture. I welded the dropout, fm adapter, and chainstay all at once. I should have the frame back in a week or two and will report back on the results.


Lichen will be releasing the Pine cycles drop outs soon. Will be another option.

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Oh sweet! That sounds like a great option, but I’m trying pretty explicitly not to step on Pine’s toes with the design I’m working on :grimacing:

To be fair, the Pine dropout is based on this dropout:

So technically you would be stepping on Long Shen’s toes :rofl:

If you could get your hands on the inserts, I think there could be a low-cost design using a laser cut plate style dropout as demonstrated by @gschwell

Good to know. Thank you

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I was just watching Letterkenny :joy:

@Daniel_Y good point! I’m much better friends with Kevin at Pine than the folks at Long Shen :wink: I’ll poke around the idea of doing a plate-style dropout. Would definitely be way cheaper than anything round/flanged.

A flat plate dropout is quick/cheap/easy for ISO mounts because it’s essentially two dimensional. I’ve had good luck with both SS and geared models. They end up costing $15-$20 for a set of dropouts. Granted, this is for my own bikes, not something I’m trying to sell.

Once you add the third dimension for the flat mount it’s going to get tricky, requiring multiple pieces to be welded/brazed with perfect alignment.

It seems like the flat mount standard is fine for plastic frames, but not so great for metal.


I use the Paragon snap ring dropouts and their flat mount bosses and machine the stay for FM160. With my benchtop mill, it took a few tries to get a rigid enough setup to make the cuts with the 5/8" end mill. It works but it’s a pain in the ass.

The other Paragon plate style options look terrible IMO. I used them when I first started building with flat mount but quickly ditched them for the a la carte option.

@Daniel_Y’s design looks like a great solution.

But I think the best solution I’ve seen so far is PVD’s Sidewinder design. It mimics the old IS standard with proprietary adapters that can work with flat and post mount calipers. It’s a really flexible system. Plus, the mounting tab is shorter than FM160, which would save on printing costs.

Really I’d love a 3d printed UDH dropout on the DS with a Sidewinder dropout on the NDS. It’d work for gravel and mountain bikes. You could run 140-180mm rotors and both caliper styles. Then get Andrew at BFS to sell them along with the adapters so they’re available to everyone. That’s the dream.


I make my own


Right on!! That looks great!

I think I’m going to try the PMW 1-1/2" dropouts with the 5/8" inserts and see how that process feels. Seems like it shouldn’t be too rough, especially once I have a mill with legible indicators :sunglasses:


I think there is one thing we all agree on:

flat mount sucks for framebuilding :sweat_smile:


I tried playing around with some plate style solutions:

Incepibicycle had a great idea using an 3D printed insert + laser cut plate:

I would guess those 3D-printed inserts cost ~$20-30 for the pair. However, with enough scale, those parts could easily be machined.

If we could get the aluminum flat-mount tab and steel dropout inserts machined, it would be a really cool plate-style architecture for flatmount.

I often find frame builders are at the mercy of the component suppliers. I am hoping that the bright minds of this forum can create our own designs and have them produced.


Isn’t that pretty much the Paragon flat mount dropout all over again, though?




Valid point :sweat_smile:

I think there is value in designing your own plate-style dropouts:

  • Cut out exact SS angles
  • hit different CS and SS diameters
  • Some people enjoy designing their own “signature” dropouts (part of the fun of building)

For people with more time than money:

  • Cannondale hanger: $10
  • Laser cut plate dropouts: $10-$20
  • pins/plates to constrain the axle $5
  • Aluminum flatmount thing $20?

Total: $55

Compared to the equivalent paragon system: $120-150

I really like Incepi’s design, because they use the Cannondale threaded hanger, which I think is one the best hanger designs for metal bikes.

Good idea on the locator pins. Its very steam punk and can still work with that cannondale hanger!

Here is a remix:

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And to match the cool plate flat mount DOs, an x-mas themed UDH DO :christmas_tree: The whole plate should probably be stainless so the rotating hanger doesn’t mar the paint. This design requires an insert that could be 3d printed or machined but anyone with a lathe could knock it out pretty quickly.

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I’ll buy some of your $55 dropouts, make 'em!



My recent design was basically this, but a little more basic. I brazed a spacer on the face of the dropout plate to get the depth, then a friend with a CNC bored the hole more precisely. They work great so far. I think it would be possible to make this design with only laser cut parts and hand finishing (for about $12).

The next iteration closer to what you show, with a shouldered piece brazed into the dropout plate, and I’m also going to recess the UDH 2.5mm into the plate.

I really like the potential standardization of the UDH, but it is clunky and obviously designed for plastic bikes where the whole body could be absorbed into the stays.

It would probably make sense to start a UDH dropout thread, I’d like to see what else people are doing. From my past research I only found on one model in the Long Shen catalog the one Paragon option. I’m guessing those of you who build for customers need to offer a UDH option once SRAM releases their direct-mount system and everyone will want the new direct-mount AXS.