What is the thread size so that I can order extra nuts?

5/16-18 (course). Fine thread would be 5/16-24. Checked with a thread gage and confirmed 5/16-18

Is there a link for a u bolt to fit a 1-3/4" od pipe, and long enough to go through 4x4 lumber and allowing for bolts and a little xtra room?

No, I've used it supporting cat5 to at giant tent in a industrial setting on 2'' conduit

What would be the one for a 6" pvc pipe?

I purchased a 2” for a 2”pipe and it fit perfectly. I assume you would therefor need a 6”

Can you please send a direct link for the u bolt that will fit around the 4”pvc pipe ?

https://www.amazon.com/National-Hardware-N222-174-2190BC-plated/dp/B000BPRP8Y/ref=psdc_16409751_t2_B000BPK8F6

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National Hardware N222-471 2193BC U Bolt in Stainless Steel

Product ID: 278092187

Details

Colour
Stainless
Exterior finish
Zinc
Head style
Cupped
Manufacturer grade
Grade 8
Material
Steel

🌊300 Series Stainless Steel Rustproof

📏0.31" Compatible Groove Diameter

🔩Grade 8 Steel Strength

$22.73

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Description

🔧 Lock in strength and style with rustproof reliability!

PRECISION FIT - Designed with Unified National Coarse (UNC) threading, perfectly tailored for US-standard applications—no metric hassles.
UNMATCHED DURABILITY - Grade 8 steel ensures maximum shear strength up to 60 ksi for heavy-duty fastening.
VERSATILE APPLICATION - Ideal for automotive, plumbing, marine, and industrial projects—engineered to perform wherever you need it.
COMPLETE FASTENING KIT - Includes plate and nuts for a secure, ready-to-install solution on pipes, wood, and more.
MARINE GRADE CORROSION RESISTANCE - Crafted from 300 series stainless steel with 18% chromium for unbeatable rust protection in outdoor and marine environments.

The National Hardware N222-471 U Bolt is a premium-grade, stainless steel fastening solution engineered for durability and corrosion resistance. Featuring Grade 8 steel strength and UNC threading, it’s designed for seamless installation on pipes and wood in demanding environments including marine and industrial settings. Complete with plate and nuts, this rust-free U bolt delivers professional-grade performance for a wide range of applications.

Specifications

ASIN	B000BPK8F6
ASIN	B000BPK8F6
Brand	National Hardware
Color	Stainless Steel
Compatible Groove Diameter	0.31 Inches
Customer Reviews	4.4 4.4 out of 5 stars (258)
Customer reviews	4.4 4.4 out of 5 stars (258)
Date First Available	16 August 2012
Exterior Finish	Zinc
Fastener Type	U Bolt
Finish Types	Stainless Steel
Global Trade Identification Number	00038613191440
Grade Rating	Grade 2
Is Discontinued By Manufacturer	No
Item Dimensions	14.2 x 10.2 x 2.5 centimeters
Item Hardness	Grade 5
Item Highlight	Rust-Free Stainless for Marine and Outdoor Mounting to Pipe or Wood; Plate and Nuts Included
Item Type Name	Stanley National Hardware N222-471 2193BC U Bolt in Stainless Steel, 5/16" x 2-1/2" x 5"
Item Weight	0.02 Pounds
Item model number	N222-471
Manufacturer	National Hardware
Manufacturer	National Hardware
Manufacturer Grade	Grade 8
Material Type	Steel
Maximum Shear Strength	50-60 ksi (345-414 MPa)
Metal Type	Stainless Steel
Model	N222-471
Number Of Items	1
Number of Packs	1
Number of Pieces	1
Outside Diameter	0.31 Inches
Part Number	N222-471
Product Dimensions	14.22 x 10.16 x 2.54 cm; 9.07 g
Screw Head Style	Cupped
Set Screw Thread Type	Unified National Coarse (UNC)
Size Name	#546-5/16"x2-1/2"x5"
Thread Class	1A
Thread Style	Right Hand
Thread Type	UNC
UPC	038613191440
Unit Count	1 Count

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