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Parker "41"
1956-1958
HISTORY
The Parker "41" is a very attractive and rather rare pen that, for some reason, long failed to attract the eye of the main collector community. It has all the features of the late-style Parker "21", and some parts are, in fact, interchangeable. It is an aerometric filler with an octanium (eight-metal alloy) nib, a steel cap and a black clip screw, and it was offered as yet another cheaper alternative to the famed Parker "51". The clip was made from heat-treated beryllium copper. It was introduced in 1956 and was positioned in a price range between the rather popular school pen the Parker "21" and the much more expensive Parker "51". In 1956, a standard Parker "51" cost $13.50, a Parker "21" $5.95, and the Parker "41" cost $8.75, or $12.75 for a matching set. The top-of-the-line Parker "61" was priced from $25.
The Parker "41" came in bright colours of pink and light turquoise and was intended to win the attraction of the ladies. There had been complaints regarding the conservative colours of the "51", but since the Parker "51" was so terrifically hyped, it turned out that few chose the Parker "41" anyway, in spite of the colouring and the lower pricing. The idea of more colourful pens was, however, later adopted in the Parker "21" and Parker "45" lines. The Parker "41" was in a way replaced by the 21 Super, in 1956, but a version survived as the Debutante, introduced in 1957, with a Parker "45"-style clip.
A selection of Parker "41"/Debutante 1956 — 1958
It seemed that women felt more comfortable with the smaller version of the Parker "51" — the Demi — also aimed at the female population. One reason for this was that the Parker "41" was made out of a more brittle plastic and could often not withstand the hard life inside women’s purses, together with keys, compacts, coins and steel hairbrushes. So, within a year, in 1958, the Debutante Parker "41" was also discontinued.
The Debutante caps were, however, re-used on the Parker "21" from 1958. They already had the correct "45"-style clip, so the switch was easy. Most Debutante "21" have been found in Dark Blue.
Differences between the Parker "21" and Parker "41":

The design of the clip, the clip of the Parker "41" was in the Parker "51" style.

The number denotation on the cap

The imprint on the filler mechanism (The Parker "41" are imprinted as such, the Parker "21's" are not)
The Parker "41" originally came in the four standard colours of grey, black, pink and turquoise, but they seem to exist in a wide range of colours. Since some parts are interchangeable, it is quite probable that Parker used old "41" stock and fitted it to "21" filling mechanisms, and vice versa, leaving both Parker "21"s and Parker "41"s in rare colours. The following Parker "41"/Debutante colours can be found in the Parker Archives:
The Parker 41 | Debutante range:

Black

Coral

Gray

Turqoise

Pale Green

Pink

Aqua
A Parker "41" with Fishscale cap, aka Debutante, 1958 Note the Parker "45"-style clip.
When the Debutante was discontinued in
1958, the white enamel cap (with a gold pattern usually referred to as the "fishscale") was instead offered on the Parker "21" range. Especially the fishscaled Debutantes are very sought after by collectors, but also the brightly coloured Parker "41"s are getting more and more popular, fetching high prices on auction sites.
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A fish scale Parker "41" Debutante, 1957
Image © courtesy of Matt McColm
A Parker ad from the time period
(Updated 2011)