WP_Model-finder.php

<?php
Class Product extends WP_Model
{
    ...
    public function _finderHeavy(){
        return [
            'posts_per_page'  => '50',
            'meta_query'	  => [
                [
                    'key'       => 'weight',
                    'value'     => 250,
                    'compare'   => '<',
                    'type'      => 'NUMERIC'
                ]
            ]
        ];
    }
}

$heavyProducts = Product::finder('heavy'); // [Product, Product, Product];