I would take them back with the bolt in my hand and ask them. After they hemandhaw get your money back and go across the street and get some Monroes. Where there is a Zone there is an Advance/O'reilly/PepBoys.

 

According to both Gabriel and Monroe, the rear shock mounting bolts are 12mm for the upper, and 14mm for the lower.

33183 :: e-Catalog :: MONROE® SHOCKS & STRUTS

Gabriel shock specs:
Product Line:Ultra ShockShock
Extended Length:15.9 in.403.86 mm.
Shock Collapsed Length:10.64 in.270.26 mm
.Length of Stroke:5.26 in133.6 mm.
Accessory Kits:n/a
Upper Mount Code:ES19 - which translates to 12mm as per their spec sheets belowLower
Mount Code:ES56 - which translates to 14mm as per their spec sheets below
Weight4 lbs.1.81 kg.Dust Tube
MaterialYesPackage Contents1 Shock

http://gabriel.com/wp-content/upload...des_051414.pdf

 

Did you read the posts in the thread? Especially #6,#7 and #8. They say that the Gabriel part is wrong.

As far as I can find both bolts are the same M12X1.75, at least for the lower.

 

Yup, looks like both those sets of shocks are built to incorrect specs for the lower mount.

This one is built to correct specs I believe: http://www.monroe.com/en-US/e-catalog/5779
- Compressed Length10.500
"Dust ShieldYes
Extended Length16.125"
Travel Length5.625"
Upper Mounting CodeLoop
Bushing& Sleeve Mount - 12MM Sleeve ID X 1.3/4" Sleeve OAL
Lower Mounting CodeLoop Bushing& Sleeve Mount - 9/16" Sleeve ID X 1.5/8" Sleeve OAL
Parts Pack(s)None
Compressed Bumper StopNoExtended
Bumper StopNoExtended
Hydraulic LockoutNoDust
Shield MaterialMeta