Safety Razor Bolt/Top Cap Threading

Created: 2020/5/7 :: Modified: 2020/5/7

Standard (10-32) vs. Metric (M5x0.8)

Some info about the differences between these two common thread sizes used in 3-piece DE razors (most of which I've gathered from various internet sources)...

There's a 5% difference in diameter and a 1% difference in thread pitch between the two.

Since M5x0.8 is a little larger, a handle threaded for it will often work with the smaller 10-32 bolt on a top cap.

However, there are cases where a maker will not follow exact tolerances, which may cause an improper fit. I have had cases where the 10-32 head feels too loose in a metric handle. I do not like to use that in shaving, because I feel there is too much pressure on too few threads.

You can use a metric tap (a machinist's tool) to enlarge #10-32 threads to make a handle likely to fit more heads.

Standard Sizes

#10-32 (SAE)

  • Merkur
  • Muhle (older, but heads were plated, which enlarged the bolt some, it seems)
  • Karve
  • Rockwell
  • Vintage Gillettes

M5 X 0.8

  • Blackland Razors
  • Charcoal Goods
  • Maggard Razors
  • Muhle (Modern)
  • Parker
  • Razorock
  • Rocnel
  • Tatara
  • Timeless
  • Vintage Gillette 3-pieces
  • Wolfman
  • Yaqi

Non-Standard Sizes

M4.5 x 0.75

  • Fatip

M5 X 0.9

  • Gibbs (French)

#8-32 (SAE)

  • Gillette Travel Tech (some models)

Unknown So Far

  • Feather AS-D2