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What Are Special Item Numbers (SINs)? Blog Feature
Ashley Mathew

By: Ashley Mathew on July 26th, 2021

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What Are Special Item Numbers (SINs)?

GSA Schedule | 5 Min Read

One of the most important things businesses need to figure out when trying to get a GSA Schedule contract is what they are trying to sell in the government marketplace. The Multiple Award Schedule (MAS) Program caters to an array of products and services, so having that initial specificity is integral to the process.

Certain identifiers, such as Special Item Numbers (SINs), are used in the MAS solicitation. But what is a SIN and why is it important in GSA Schedule contracting? Throughout the course of this post, we will be covering what a SIN is, why it’s important, and how to determine what your SIN could be.

What is a Special Item Number (SIN)?

A Special Item Number (SIN) refers to certain products or services a GSA contractor offers to government buyers. Changes to GSA regulations and the MAS solicitation in recent years has modified SINs to align with North American Industry Classification System (NAICS) codes, making the identification process easier for contractors and administrators.

Within the vast world of the GSA MAS Program, the solicitation is broken into 12 Large Categories, then subcategories, and then further narrowed down to 315 SINs with their corresponding NAICS codes. By categorizing solutions, it becomes easier for potential buyers to search goods or services depending on their needs.

GSA gives contractors the opportunity to self-certify themselves, allowing them to place themselves under certain subgroups, given they meet another layer of qualifications. Choosing subgroups under the SINs on your contract allows businesses to potentially grow their reach to buyers within the public sphere.

As an example, let’s say your company is trying to sell pens on the market. This would fall under Large Category A, also known as Office Management. Within this category, there are several Subcategories, including Office Supplies. The list then narrows into the designated SINs under this category. SIN number 339940 aligns with office products, but within this SIN there are other subgroups such as “Shredders,” “Toner Cartridges,” and even “Desk Supplies,” a category which pens would fall under. Creating that specificity allows potential buyers to have an easier time researching sellers based off their given needs.

Why Are Special Item Numbers (SINs) Important?

SINs are also integral to contractors post-award. Once awarded a GSA Schedule, businesses have access to tools that will allow them to see specific agency requests and needs. GSA’s eBuy system is an electronic Request for Quote (RFQ) or Request for Proposal (RFP) system which allows government buyers to request information and quotes for services and large purchases.

Buyers send out their RFQs/RFPs based off the necessary SIN(s), sending alerts to respective businesses and contractors. This means if a business offers a service or product that is not a listed SIN on their contract, they are unable to view potential opportunities. The buying process is part of the reason it’s important to make sure your contract SIN(s) are accurate and updated.

In addition to general marketing purposes, it becomes easier for GSA to keep track of different businesses and items offered within their system. The federal government is the largest buyer of products and services in the world, and there is a plethora of products, contracts, and services housed within GSA, which is part of the reason why organization is so important.

How Do I Determine My Special Item Number (SINs)?

When determining what products/services you would like to sell, the next step is to figure out what categories and respective SIN(s) they correspond to. GSA has an “Available Offerings Attachment” listed on their website which identifies the Large Categories, Subcategories, and SINs currently available through the MAS Program.

There are 315 SINs available to GSA Schedule contractors, which range from grounds maintenance, to travel, to consulting services. GSA constantly monitors the market to add new products and services, meaning that updates to the solicitation in the future could add more SINs to the catalogue. It’s important to have the appropriate SINs for your given products or services. If not, your GSA proposal will most likely be rejected.

Depending on the category, some SINs have certain requirements that need to be met in order to be approved and sell in the government market. For example, GSA’s Highly Adaptive Cybersecurity Services (HACS) SIN, listed under Information Technology Large Category F, requires provided labor categories, descriptions of two past projects, and participation in an oral technical evaluation conducted by a Technical Evaluation Board (TEB).

Where Can I Find a List of SINs?

For those interested, SIN descriptions are available on All you need to do is download the attachments that correspond the respective categories you think your products would fall under, and the corresponding SINs are included. Descriptions are also listed on GSA eLibrary under the “Category Guide” section as seen in the photo below. When clicking under the respective links, SIN descriptions that fall under that category will appear. It also allows viewers to see eligible contractors within each SIN, giving greater insight into the market and who your competitors are.

Can I Add/Delete SINs to My GSA Schedule?

As your business changes and becomes more acquainted with the federal marketplace, you may want to expand or minimize the products and services you offer. Under the new MAS consolidation, contractors can add more SINs to the GSA Schedule than ever before, provided they are able to meet the requirements. Several types of modifications can be made to your GSA Schedule, two of which include adding or deleting products/services to your contract. Our team of Winvale consultants are more than able to assist your business in the modification process.

Do You Have Any Questions About Special Item Numbers (SINs)?

Determining your SINs is important in understanding the market and the potential customers you may have. Given the sheer number of options and ranges, navigating through SINs can be a difficult process. If you would like more information on the world of SINs, check out our other blogs related to the topic such as “How to Choose the Right SIN and Avoid GSA Rejection”, “Four Tips for Preparing a Successful GSA MAS Offer,” and many more. If you have more questions about your GSA contract, our team at Winvale is here to help.

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About Ashley Mathew

Ashley Mathew is a consultant in Winvale’s Philadelphia office. Ashley is a native of the Greater Philadelphia area and a graduate from Messiah University with a Bachelor of Arts degree in Political Science and International Relations.