1 and 6-hole cap styles.

[Greg G.]

The receiver shell on my 151-AL is a repro, so that's getting replaced.  The cap seemed original, but to make sure I compared it with known originals I have, and I noticed a different hole pattern in some of them.  One hotel phone I have has the one large hole, but another had a cap with 6 small holes.  My other sticks are the same way, one with a 6-hole cap and another with 1-hole.  When did they change the hole styles on these?

[rdelius]

the 6 hole is on a 706 capsule receiver.Most likely mid 30s when F1 was developed.Note wavy where ear touches

[Sargeguy]

They are also made out of plastic.