Source

File: wp-admin/includes/class-wp-screen.php

public function render_screen_layout() {
		if ( ! $this->get_option( 'layout_columns' ) ) {
			return;
		}

		$screen_layout_columns = $this->get_columns();
		$num                   = $this->get_option( 'layout_columns', 'max' );

		?>
		<fieldset class='columns-prefs'>
		<legend class="screen-layout"><?php _e( 'Layout' ); ?></legend>
		<?php for ( $i = 1; $i <= $num; ++$i ) : ?>
			<label class="columns-prefs-<?php echo $i; ?>">
			<input type='radio' name='screen_columns' value='<?php echo esc_attr( $i ); ?>' <?php checked( $screen_layout_columns, $i ); ?> />
			<?php
				printf(
					/* translators: %s: Number of columns on the page. */
					_n( '%s column', '%s columns', $i ),
					number_format_i18n( $i )
				);
			?>
			</label>
		<?php endfor; ?>
		</fieldset>
		<?php
	}