Short answer: "Type XXI 3817" is a search phrase shoppers use for the Longines Avigation Type XXI pilot chronograph family, and a "fake Type XXI 3817" is a replica built to imitate it. The pick that holds up best in person is a stainless-steel automatic copy with working chronograph pushers, a matte black dial and a case sized close to the original proportions. The criteria behind that pick are dial printing, case finishing, movement type and caseback engraving, in that order.
What the Reference Number Tells You
Longines files its vintage-inspired pilot chronographs under the Avigation and Heritage lines, and reference numbers in that range describe one specific combination of case, dial and caliber. A number typed into a marketplace listing proves nothing on its own. Confirm the reference against the Longines catalog or a reference database first, then compare that confirmed layout to the watch in front of you. If the seller cannot tell you which caliber the original used, the listing is guesswork.
Tier 1: Quartz Copies
Pros
- Lowest entry cost and easy to replace
- No winding, no service, works after months in a drawer
- Light on the wrist for stage or photo work
Cons
- Seconds hand ticks instead of sweeping, which is the first giveaway
- Subdials are often printed or frozen rather than functional
- Case and bracelet feel hollow, and plating wears through at the lugs
Use case: costume, film props and short photo shoots where nobody inspects the watch at arm's length.
Tier 2: Automatic Copies With a Modified Chronograph Movement
Pros
- Sweeping seconds and pushers that actually start, stop and reset
- Closer case thickness and weight to the original
- Standard lug width, so aftermarket straps fit without filing
Cons
- Case is usually a millimeter or two thicker than the source model
- Rotor noise and rough winding feel show up on cheaper examples
- Servicing a modified chronograph movement is awkward outside specialty shops
Use case: daily wear for someone who wants the pilot chronograph look and will accept a service headache later.
Tier 3: High-End Custom Builds
Pros
- Case dimensions, bezel profile and hand shapes that match the source closely
- Sharper dial printing, better anti-reflective coating and cleaner lume application
- Correct-style caseback engraving and a properly tapered strap
Cons
- Cost can approach a used entry-level Swiss watch, which changes the math
- Sellers inflate claims, and paperwork rarely means anything
- No manufacturer warranty, and resale value is near zero
Use case: a buyer who knows it is a copy, wants the closest visual match, and keeps the purchase honest. Never accept one of these sold as an original.
Criterion: Dial and Hands
Compare subdial spacing, date window position and text weight against a confirmed photo. Soft or doubled printing, a flat painted date wheel and hands with rough edges are the usual tells.
Criterion: Case and Bezel
Check lug shape, crown guards and pusher profile. A brushed finish that runs into polished edges with no crisp line means the case was finished after assembly, not before.
Criterion: Caseback and Strap
Engraving should be cut, not laser-printed on the surface. Strap stitching, taper and buckle stamping are cheap to fix, and sellers rarely bother.
Quick Checklist Before You Pay
- Confirm the reference against an official catalog or database.
- Ask for a video showing the chronograph running and resetting.
- Request a straight-on dial photo and a side profile shot.
- Ask what movement is inside and whether the subdials are functional.
- Confirm the return policy in writing before payment.
Which Tier to Choose
Buy Tier 1 only for costumes. Buy Tier 2 for regular wear if the chronograph works and the case sits close to the source dimensions. Consider Tier 3 only when the visual details matter more to you than warranty or resale. If you want a genuine example, buy from an authorized dealer or a service-backed listing instead of gambling on a marketplace.