Capstan bars are wooden poles used to turn capstans. One end of each capstan bar is squared off to fit into the square hole in the capstan drumhead and the body is round to make it easy for the sailors to grab the bar. Some bars also had a ball at the end opposite the square end. See the following figure from the Paasch encyclopedia.<![if !supportFootnotes]><![endif]>
Paasch Marine Encyclopedia, portion of plate 67
The length of the bars depended on the clearance around the capstan it was used with – the bars were as long as they could be and still clear all obstructions as the capstan rotated.
The bars were stored, generally on racks, when not in use. The Boucher MFA model and most plans show the bars for the poop capstans were stored on racks on the aft of the poop portico. The Boucher MFA model shows the bars for the capstan at the aft of the main deck on racks around the main mast, see figure below: (the bars are hard to see but there are 3 darker brown bars on the side of the mast)
Main mast of the Boucher 1916 model of the Flying Cloud
This location is similar to the racks around the foremast shown in the following photograph of the Sea Witch.
The foremast of the Sea Witch in the 1880s showing the capstan bars
Neither the Boucher MFA model nor any of the sets of Flying Cloud plans I have found shows the storage for the bars for the capstan on the forecastle but Magoun says that the rack was Òalong the bulwarksÓ. (He says the same for the aft main deck capstan bars)<![if !supportFootnotes]><![endif]>
<![if !supportFootnotes]><![endif]> Heinrich Paasch, Illustrated marine Encyclopedia (1890), plate 67
<![if !supportFootnotes]><![endif]> F. Alexander Magoun, Frigate Constitution and other historic ships (1928), page 128