woocommerce_product_thumbnails_columns filter-hook . WC 1.0

Usage

add_filter( 'woocommerce_product_thumbnails_columns', 'filter_function_name_9016' );
function filter_function_name_9016( $4 ){
	// filter...

	return $4;
}

$4

-

Where the hook is called

$columns           = apply_filters( 'woocommerce_product_thumbnails_columns', 4 );

Where in WP core the hook is used WooCommerce