Looking for the correct wheel bolt?

[Dodgefran]

I've got a 1938 Dodge RC Humpback Panel Truck and no rear wheel bolts.  with this truck, the bolt screws into the drum.  I have measured the opening with my caliper and it shows 7/16 ".  All of the wheel bolts that I have bought from the web sites are 1/2" thick.   Where did I go wrong.   I bought this truck totally stripped.  So I don't have any samples.  The original part numbers are 571810 (rt rear) and 5571811 (lft rear)out of the 1938 parts book.

Can anyone help with this?  Thank you

[joe_padavano]

If you are using a caliper to measure the inside diameter of a threaded hole, you are measuring the tap drill diameter, not the bolt diameter. The tap drill is the diameter of the hole you drill in the part before you cut the threads. The tap drill for a 1/2-20 fine thread fastener is 0.4531". The decimal equivalent of 7/16 is 0.4375". If you don't have thread gauges, get a 1/2-20 bolt from the hardware store and see if it threads into the RH side (the LH side is LH thread).

 

[CarlLaFong]

Mopar used those lug bolts for years and years. There must be a gazillion of them out there. Post on a Mopar specific forum

[JFranklin]

Stop in at a NAPA store, maybe they can help you.

[28 Chrysler]

Left and right hand threads were used   (left on the left, right on the right)

[Dodgefran]

On 7/10/2021 at 7:24 PM, joe_padavano said:

If you are using a caliper to measure the inside diameter of a threaded hole, you are measuring the tap drill diameter, not the bolt diameter. The tap drill is the diameter of the hole you drill in the part before you cut the threads. The tap drill for a 1/2-20 fine thread fastener is 0.4531". The decimal equivalent of 7/16 is 0.4375". If you don't have thread gauges, get a 1/2-20 bolt from the hardware store and see if it threads into the RH side (the LH side is LH thread).

 

Thank you joe_padavano.  Thanks for catching that.  That's info that a beginner needs to know.  Then I do have the right size.  I tried to hand tighten one in a few holes ,rt side and lft, and it wouldn't bite so I might have to go the rust rout.  I'll try that first.  Thanks to all who answered

[joe_padavano]

Be sure you're trying a RH thread bolt on the RH side of the car and a LH thread bolt on the LH side of the car.

I'd suggest chasing the threads with a tap, but you'll probably pay dearly for a LH 1/2-20 tap from a place like McMaster Carr. At least the threads on the RH side are RH thread.

[mike6024]

I always check eBay for odd stuff like that, 

 

1/2-20 UNF Tap Left Hand Thread 1/2"-20 TPI

 

US Stock New HSS 1/2-20 UNF Tap Left Hand Thread 1/2"-20 TPI High Quality M830
Condition:New
Quantity:
1
8 available / 66 sold
Price:
US $10.99

[Rusty_OToole]

You want a thread chaser not a tap, a tap can enlarge the hole. You can make a thread chaser by grinding a groove in a bolt if you can't find one. Maybe a wire brush would clean the hole, like the kind you use to clean battery clamps?