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The feature that distinguished [[Esterbrook]] production was the interchangeable nib unit,<ref>this feature was protected by the patents {{Cite patent|US|1939753}} and {{Cite patent|US|1939753}} registered respectively in 1933 and 1935, but applied in 1928 and 1933.</ref> but it wasn't the first company offering this feature, that was already used by the [[Personal Point]] nibs made by [[Wahl Eversharp]]. Differently from [[Eversharp]], [[Esterbrook]] used the feature to consent to its clients to easily change their nib as they please, in any moment and not just when buying the pen, helped by the low price of its cheap steel nibs.

The feature that distinguished [[Esterbrook]] production was the interchangeable nib unit,<ref>this feature was protected by the patents {{Cite patent|US|1939753}} and {{Cite patent|US|1999177}} registered respectively in 1933 and 1935, but applied in 1928 and 1933.</ref> but it wasn't the first company offering this feature, that was already used by the [[Personal Point]] nibs made by [[Wahl Eversharp]]. Differently from [[Eversharp]], [[Esterbrook]] used the feature to consent to its clients to easily change their nib as they please, in any moment and not just when buying the pen, helped by the low price of its cheap steel nibs.

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