What size wire is used in comic book staples?

For Silver Age comics (typical 32–36pp saddle-stitched booklets), the staple wire was generally round, galvanized “stitching wire” in the ~24–26 gauge neighborhood, with #25 being the most common “standard” size in saddle-stitching operations.  

Typical diameters for those stitching-wire gauges are:

• #24: ~0.0230 in (≈ 0.60 mm)  
• #25: ~0.0217 in (≈ 0.55 mm)  
• #26: ~0.0204 in (≈ 0.51 mm)  

For translating that into AWG (electrical) just for intuition, 0.51–0.60 mm is roughly AWG 24 to AWG 23-ish by diameter.

Golden Age comics were saddle-stitched with round “stitching wire” that’s typically about 0.50–0.60 mm in diameter (≈ 0.020–0.024 in).  

In “stitching wire” numbering that’s commonly No. 26 (0.50 mm) up to No. 24 (0.60 mm).  

If you want it in rough AWG terms, that diameter range lines up around ~23–24 AWG (with 0.60 mm drifting a bit thicker). And yes—wire gauge is one of those “bigger number = thinner wire” traditions we’ve all agreed not to question.