There is no difference between these bolts. The “X”, “SC”, and “N” simply identify the type of connection the bolts are used in. “X” and “N” are bearing type connections, where the bolts are being used in shear.
“X” means these particular A325 heavy hex structural bolts will be used in a bearing type connection where the threads will be excluded from the shear plane, whereas “N” means the threads are included in the shear plane. “SC” signifies a slip-critical connection where the bolts are not being used in shear, but instead, the tension from the connection resists the shearing force. You simply require the same standard A325 heavy hex structural bolt but will be using them in three different connection types.
| SC | Slip-critical connection. |
|---|---|
| N | Bearing type connection with threads included in the shear plane. |
| X | Bearing-type connection with threads excluded from the shear plane. |
“SC”, “N”, and “X” specify solely the type of connections to use the A325 bolt in.
According to Note 2 in Section 3.8 (Ordering Information) of the new F3125 specification covering high strength structural bolts, “Bolts are sometimes detailed with names such as A325 HS, A325 SC, A325 x or A490 N. These names relate to connection design and bolt installation, but do not change the manufacturing requirements and are preferably not shown on bolt orders.”
There are other types of A325 bolts that do affect the type of bolt that needs to be purchased. For these, see the following chart.
| TYPE 1 | Medium carbon, carbon boron, or medium carbon alloy steel. |
|---|---|
| TYPE 2 | Withdrawn November 1991. |
| TYPE 3 | Weathering steel. |
| T | Fully threaded A325. (Restricted to 4 times the diameter in length) |
| M | Metric A325. |
| S | Modified thread length or head dimensions. |
The majority of A325 bolts being made in the market are A325 Type 1 and are available both plain and hot-dipped galvanized. Type 2 was withdrawn in 1991 and no longer is in use. Type 3 is a naturally corrosion-resistant weathering steel that typically is used in a plain finish (no finish). Availability for the steel can be limited and standard, mass-produced bolts start at 5/8″ diameter. Below 5/8″ diameter, heat-treatable weathering steel is not commonly available.
A325T bolts (covered under supplementary requirement (S1) of the A325 specification signifies that the A325 bolt must be completely threaded, but is limited to 4 times the diameter in length. Fully threaded A325 bolts longer than 4 times the diameter do not comply with the specification, will not be available in the marketplace, and technically cannot be manufactured. ASTM A449 should be considered in lieu of A325 bolts with extended threads that don’t meet the requirements of A325T. However, ASTM 3125, the new combined high strength structural bolting specification, added a new type S that allows for an A325 bolt to have altered thread length and head dimensions. Previously, altered thread lengths meant switching grades or accepting a bolt that didn’t technically conform to the A325 specification, but now marking the bolt head with an S allows for extended threads or using different head dimensions.
The connection information provided in this FAQ is applicable to not only A325 heavy hex structural bolts, but to A490 structural bolts as well.
What is the maximum and minimum available bolt lengths for tc bolts and non tc bolts
@Sridhar- The available lengths will vary depending on the bolt diameter. Additionally, we are able to manufacture custom lengths on some grades and styles.
what makes the designer to choese N bolts instead of x bolts ???
@Balasaheb- Our only guess would be that the designer, after looking at all the information, decided that including the threads in the shear plane was not detrimental to the integrity of the structure.
Is there installation difference between for X and N? Say if I design it for X, how do it know it is end up N or X?
@James- The installation method is the same, but for X type connection, the designer needs to make sure that the threads are excluded from the shear plane, so a longer bolt may be needed. For N type connections, threads are allowed in the shear plane, so the only concern is that the bolt is long enough to stick through enough to fully tension. If you design for X, you will need to make sure that the bolts are long enough that only the unthreaded shank is in the shear plane. That can be done by specifying the correct length of bolt, taking into account the thread length. Additional washers can also be added if necessary, in case the longer bolt means that the threads end before the nut is fully tensioned.
In A325N bolts threads included in shear plane. Is it affect the bolt strength?
@Karthick- The threads in the shear plane will affect the bolt’s shear capacity since the minor diameter of the threads is smaller than that of the unthreaded shank. The tension capacity is not affected.
Hi,
In one project, Engineer’s has recommended using TC Bolts at the connections. But due to insufficient access for Tensioning Gun, can we used the Turn of Nut method on TC Bolts.
@Jeff- Using a TC bolt without the matching gun is highly unusual and we are not certain if you could achieve the proper tension. We are not in a position to say one way or the other if it will be acceptable in your situation, you would need to pass it by the project engineer.