Chain grades and links explained

By Michael Reardon

When selecting anchor or windlass chain, there are 4 basic considerations:

• Grade (metal tensile strength)
• Diameter (thickness of chain)
• Coil (opening size)
• Finish (corrosion resistance)

Chain Grade

Grade refers to the tensile strength of the metal. The grade number used by manufacturers indicates the ultimate break strength of chain. The higher the grade, the greater the break strength. With galvanized chain, it basically boils down to how much carbon is in the steel. Grade 30, aka proof coil, has less carbon and is good service duty chain. Grade 43 chain (aka Grade 40) has higher tensile strength and abrasion resistance and comes with a higher price tag.

The grade refers to the tensile strength of the chain. This is expressed in newtons per square millimeter (a newton is approximately 0.224805 lbs). The tensile strength is calculated by multiplying the grade times the area of the two cross sections of a link (see above).  (Area) 157.08 mm2 x 800 n (Grade)=125,664 newtons ultimate breaking strength 125,664 newtons x .224805=28,250 lbs ultimate breaking strength 125,664 newtons/1000=125.66 kn (Kilonewtons)

Proof Coil

Proof coil, also known as Common Coil chain, is the standard commercial quality regularly stocked by hardware and industrial supply houses. Proof coil is grade 30 chain, a general purpose chain for pulling or restraining applications. Proof coil is not for overhead lifting or where maximum tensile nor impact strength is crucial. Basic carbon steel metal composition makes it the go-to for log chains and towing. This metal can look different depending on finish. Standard Finishes may be plain, colored, bright zinc or hot dip galvanized. Because tolerances aren't as tight for inconsistencies in link size and diameter with proof coil, the cost is less than precision chain such as BBB for windlasses.

Chain Link Size

Chain link openings vary, too. We offer chain with elongated link sized called Long link. This is a practical choice where connections must fit mid-chain, not the end link. With the longer links, shackles bolts fit anywhere along its length, whereas standard coil sizes may only fit shackles on end links. Long link also makes the chain lighter than an equivalent length of standard chain.

BBB chain is a compact link style often of standard commercial quality such as Grade 30 or 43. Made from low carbon steel, this chain is used primarily for boat windlasses when hot galvanized. The wildcat of any windlass must mate with chain link size exactly (think bicycle chain), so be sure to check with windlass manufacturer.

Another link variation is studded chain, also called tugboat chain. Studded link means the wire forming each link also spans across the middle of link opening, making it extremely heavy and strong. Studded is for large diameter chain. If you have a boat 60 feet or above you may used studded link on the ground tackle for added weight and strength.

Finish

The most common metal finish, 'hot dip' galvanized steel, works best for salt water use. Stainless steel is preferable on deck and is sometimes used for bright polished aesthetic anchor chain. Hot dipped galvanized is preferred for chain remaining underwater. Stainless steel needs oxygen to breathe. Constantly submerged, the lack of oxygen is thought to cause stainless steel to corrode. What is galvanized or hot dip galvanized? Steel is 'hot dip galvanized' in a bath of zinc at over 800°F. The resulting molecular alloy exterior yields a very corrosion-resistant metal. The most common chain for mooring use is a hot dip galvanized Grade 30 proof coil. The most common for anchoring is hot dip galvanized BBB.