These arms mate with Cannondale's Hollowgram Bottom Bracket spindle, which is 30mm in diameter.  they make many widths:  109mm, 119, 125, 137, 160, 166mm.  It can fit on road, cx, gravel, xc, trail, freeride, and downhill bikes.  

The complete crankset works with BB30 bottom brackets as well as BB30a, PF30, PF30a, BBRight, Specializled OSBB carbon and aluminum, BB386evo, BB86, BB92, T47, and T47a.  The company Wheels MFG has bottom brackets that work with all of the above.  

The 130mm spindle is removable.  You can install any number of spindles, a 135mm for older Campagnolo chainrings, a 110 for modern 5-bolt rings, few four-arm spiders for road rings (including a 120/90 setup for adventure gearing), a few four-arm spider for mtb rings (120/84 and 104/64), as well as spiders for 1x ring setups, a 104mm spider for triple-ring setups, too.  There are even direct-mount rings, both in single ring and double-ring setups.  

These arms are light.  The left is 161g, the right 227g.  Built up with spindle, 53/39 rings, bearings, spacers, bolts, the set can be as light as 675g.  And they're stiff.  Hollow arms are the key.

These arms are in decent shape.  They are functionally great, but there is some scuffing from ankle striking and such over time.  The wear marks could be buffed out if you want them to have that new look.  The nice thing about the silver arms over the newer Black ones is that the silver doesn't wear off the way black anodizing does.  All the same, if you get them nice and want to protect them, Crankskins has you covered.  

If you aren't already a convert, you'll also need to pocure two crankarm fixing bolts, a BB30 spindle, a removal tool to get the arms off the spindle, bearings (if you aren't buying a complete BB, dust covers, and spacers.