SELECT jm_posts.* FROM jm_posts 
INNER JOIN jm_postmeta as thid ON jm_posts.ID = thid.post_id 
INNER JOIN jm_postmeta as thmeta ON thmeta.post_id = thid.meta_value 
WHERE 1 = 1
AND thid.meta_key = '_thumbnail_id'
AND thmeta.meta_key = '_wp_attachment_metadata'
AND thmeta.meta_value LIKE '%s:7:"grid170";%'
LIMIT 10

<?php

add_filter( 'query_vars', 'thsize_query_vars' );
function thsize_query_vars( $vars ) {
    $vars[] = 'thsize';
    return $vars;
}

add_filter( 'posts_join', 'thsize_join_clauses', 10, 2 );
function thsize_join_clauses( $join, $q ) {
    if ( isset( $q->query_vars['thsize'] ) ) {
        global $wpdb;
        $join .= " INNER JOIN {$wpdb->postmeta} as th_id ON {$wpdb->posts}.ID = th_id.post_id";
        $join .= " INNER JOIN {$wpdb->postmeta} as th_meta ON th_meta.post_id = th_id.meta_value";
    }
    return $join;
}

add_filter( 'posts_where', 'thsize_where_clauses', 10, 2 );
function thsize_where_clauses( $where, $q ) {
    if ( isset( $q->query_vars['thsize'] ) ) {
        $th_size = $q->query_vars['thsize'];
        $th_size_serialized = serialize( $th_size );
    
        global $wpdb;
        $where .= " AND th_id.meta_key = '_thumbnail_id'";
        $where .= " AND th_meta.meta_key = '_wp_attachment_metadata'";
        $where .= " AND th_meta.meta_value LIKE '%{$th_size_serialized}%'";
    }
    return $where;
}

<?php

$posts = get_posts( array(
    'post_type' => 'any',
    'thsize'    => 'grid170',
    'post_type' => 'post',
    'suppress_filters' => false, // to pass in required hooks
) );