The 88351-S8 studs arrived yesterday, but they don't fit. Although the OAL of 7/8 is correct, I think the zinc plating is preventing them from being screwed into the retainer. I double checked them by attempting to put a 5/16-18 nut on, but wouldn't work. The Dorman studs that I had previously bought fit the retainer, but they are 3/8 longer at 1 1 1/4. I will use the Dorman studs and hope that the extra length won't be a problem. 

I sent an email to Hill's, requested a refund, and told them to check their stock before fulfilling any more orders for the studs.                                                                                                                              

88351-S8 is the correct part number for the studs. Tim Hill said that they weren't included in their catalog/website due to low demand, but both will be updated. NPD has them, same part number. 

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According to Tim Hill, the oil-pan-to-retainer stud part number is 88351-S8; however, it could not be found on Hill's Thunderbird site. I then did a web search of the part number and found it on NPD's site. The studs cost $2.06 each, but shipping will exceed the cost of the studs. Nuts & washers are not included. 

FYI: The specifications listed by Dorman for the 23733 stud kit is incorrect. One end is 5/16-18 and the other 5/16-24 (as they should be); however, Dorman says that the 5/16-18 end is 7/16 while the 5/16-24 end is 5/8; this is backwards. The 5/16-18 end is 5/8 while the pan end is 7/16. The specified OAL of 1 1/4 is correct, but the included nuts are 5/16-18; they should be 5/16-24.One other thing: Dorman's photo displays zinc-plated studs, but they are black oxide. 

I've sent an email to Dorman's Customer Service and pointed out the error. Unfortunately, retailers are using Dorman's specifications. 

Thanks, Richard. I had already ordered Dorman 23733 Water Pump Stud Kit from Walmart. The retainer cap end is 5/16-18 x 7/16 and the pan end is 5/16-24 x 5/8. OAL is 1 1/4. It hasn't arrived yet, but I guess it will do. 

Blackie,
I had ordered an assortment of  studs. 7/8 1 1/4  1 1/2. I can return the ones I don’t use.  

Blackie,
I had ordered an assortment of  studs. 7/8 1 1/4  1 1/2. I can return the ones I don’t use.  

OPPs it was 9l16 lower and 7/8 upper in length
they also have 3/4
my search was 5/16 double ended stud 

I just went to Amazon's site and searched 5/16-18 x 3/4 and found nothing that size. Is 3/4ths long enough?