Hi, the thread on the IRD filler are stripped, am thinking of helicoiling it, could someone please tell me what size helicoil to use. Thanks

M18, springs to mind, but surely the best way to find out, would be to measure the thread size on a new plug? Never actually seen one where the IRD thread is damaged, as the plug is much softer than the IRD casing.

Thanks for the reply. I decided to change the oil, it didn't feel right when I was taking it out, I had a new plug and washer ready to replace it, and the new one won't tighten, any advice would be welcome.

I had the same issue about four years ago and successfully helicoiled using a 22.5mm drill to clear the hole, then a M22x1.5 tap. I can't see what size the actual helicoil is as the label on my packet has deteriorated but there are tables online that will give you that information. But these sizes enable the original filler plug to be used. I remember that I had to do a lot of research online to find the correct elements.

If you were closer I'd lend you my drill and tap as they're expensive for what is likely a one time use, but maybe you've already got that level of equipment. What I can do, if you have any problems working out the helicoil, is send you one of mine. I had to buy a packet of five, so I have four spare. Best of luck.