Add a label on shop page results

Hi, I’ve added a custom php snippet in my themes functions.php to show the SKU number on the products display on the shop page. This works but I’d like to add the text ‘Parts Number’ before the SKU number. I’m not too clever with php coding, this is a snippet I found by searching. Can anyone please help? Many thanks

add_action( 'woocommerce_after_shop_loop_item_title',  'custom_after_title' );
function custom_after_title() {

global $product;

if ( $product->get_sku() ) {
    echo $product->get_sku();
}

}

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