I've been looking to get a variety pack of metric cap screws, various lengths and diameters etc. Does anyone have a source for something like this?

Local small hardware stores may or may not have a section of by-the-piece hardware. You should be able to find black oxide M4, M5, and M6 bolts in various sizes. Certain big box locations have 'expanded' selections that may include metric cap bolts of various sizes and lengths. Finding a stainless bolt will be harder than a less corrosion resistant black oxide bolt, but that only matters if the bolts will be damp/wet for long periods, or subjected to 'extreme' conditions like salt spray or bog water. Peter White cycles sells bolts of various sizes by the piece, but they have a shipping minimum. It's better to call them for the order once you bought enough. I really like the connex chains they sell, but I only used the wider chains. Your LBS may carry stainless bolts, but many of the silver bolts my LBS sells are galvanized, which is good enough.

Importantly, know your bolt diameter and thread pitch. Ideally, bring a bolt with you that you know works for your application.

Ace Hardware seems to have the best selection of stainless metric fasteners of hardware stores. Barring that, google ‘fasteners’ and see if there’s a fastener supplier in your area. That’s the most comprehensive source of supply.

You do want stainless hardware.

McMaster Carr.

Yes, along with Grainger, Fasteners Inc and Fastenall.

Marine supply places have good selections of stainless hardware. Here's one in my area.

https://catalog.monroeengineering.co...l-a2-metric--2

My go-to for ordering fasteners online is boltdepot.com.

They seem to stock just about every size and shape.

The Ace & True Value have these at reasonable prices in Albuquerque, as did Busy Bee in Santa Monica, B&B in Venice (CA). I'd expect them at all self-respecting hardware stores.

I recommend Totally Stainless. Download their catalog and you'll see you can order stainless steel metric cap screws in high or low strength with many head styles and in just about every thread and length: Shop Totally Stainless.com - Home

They are old school but they have the best in stainless steel hardware.

McMaster has assortments.

https://www.mcmaster.com/metric-screw-assortments

I bought a variety of sizes of bolts from them a few years ago and haven't yet had to replenish. Shipping prices weren't good is the downside to bolt depot.
Glanced at a new local Ace and was impressed with selection of stainless metric stuff.

My local Ace Hardware has a very good selection of black and plain bolts (metric or English). The local Fastenal has stainless, and seems to welcome walk-in retail shoppers, although I've been to other locations that are more like the local Grainger: if you're not commercial, you're not welcome.

Shop around your town and see who's got what (and will sell it to you!).

Friendly with your LBS? All the mechanics will have drawers full of them. Small favors go a long way.

I've decided to put button head screws/bolts on my Fargo. They'll make it so much more aero! Actually, I just don't want to get scraped/gouged by a cap head screw in a crash.

McMaster-Carr has a pack of fifty for around $7. Maybe not that good of a deal, but I'll tack it onto another order, so it'll be essentially free shipping.

Zinc plated, T25. I figure torx beats 3mm hex, and I'll be carrying a T25 wrench for the brake rotors bolts anyway. Maybe the post mounts too. Given all the barnacles on the Fargo, that'll be over twenty bolts right there except for the two extra long ones I have under the downtube.

I'm visiting family in New Orleans area, and recently the Fastenals around here imposed a $100 minimum purchase requirement.

scott s.
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That's a lot of screws

I'm not sure if the proper response is "ouch" or "screw them."

I don't understand some of these business models. Grainger here won't sell to an individual, but I've bought <$10 of goods from them using a corporate credit card (but I told them it was for work. Yes, to make my bike work.) My local Fastenal sold me a single allen wrench and half a dozen single bolts, but when I needed a replacement bolt out in Arizona, I had to buy a package. We used to have a wholesale screw and nut store in town; they'd sell me half a dozen grade 5 single bolts as long as I bought a box of some screws, so I bought a box of wood screws. How do those policies make sense?