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Space bar is the key on a keyboard used to enter the space character.
A single press on the Space bar enters a single space character (ASCII 0x20).
Alt Gr+Space (or Control+⇧ Shift+Space) often enters a non-breaking space character (Unicode 0xA0).
As most users only press one part of the space bar, some keyboards split the space bar to allow some of the wasted space to be repurposed. The Filco Minila divides the space bar into three, with the first and third segment optionally mapped as the Fn key. NMB used a split space bar for their Erase-Eaze facility.
A new keyboard layout called "SpaceFN" has recently been mooted, which allows the user to treat the entire space bar as the Fn key, with the space character being generated only if space bar is pressed and released without any intermediate keystrokes being detected.
Dimensions and mounts
The size of the space bar varies by keyboard. On some vintage keyboards, the space bar is almost the same width as the entire alphanumeric area. On modern Western keyboards, space bar is typically between 6 and 7 units wide, being by far still the widest key on the keyboard. As the Japanese language does not use spaces, the space bar on Japanese keyboards is fairly small, often as small as left shift.
The width of the space keycap and the positions of the mounts—the pegs or slots where the keycap attaches to the switch and the stabilisers—varies between keyboard, even between keyboards that use the same switches. These differences cause problems with purchasing aftermarket keycaps, as the space bar from a particular keycap set may not fit the keyboard for which the purchase was intended. Unlike other keycaps where the differences are fairly small in number (e.g. ISO vs ANSI left shift, 1.25 or 1.5-unit modifiers), the space bar varies in dimensions significantly.
On many keyboards, space bar is more heavily weighted than the remaining switches. Topre use an additional helical spring under the space bar of their Realforce keyboards to increase the weight. Alps SKCL/SKCM-based keyboards typically use the same switch for space, but Alps did produce higher rated switches for this purpose. Cherry produced a set of special grey-coloured switches (Cherry MX Linear Grey, Tactile Grey and Click Grey) for use under space bars on Cherry MX-based keyboards.
Separate space bar switch type on an Hi-Tek Series 725 keyboard