If you’re a spare parts supplier (like me, been in the game for 12+ years) or a shop that’s got a warehouse full of those tiny, easy-to-lose-but-critical bits, you’ve definitely been stuck between two nightmares: overstocking a part that sits on shelves collecting dust and eating cash, or running out of something that a customer needs right now and losing their business. Let me tell you, balancing spare parts inventory isn’t just a spreadsheet math problem—it’s a mix of listening to your customers, knowing your parts, and being okay with tweaking things when stuff changes. No fancy MBA jargon, just the stuff that actually works for someone like me who’s shipping parts to factories, repair shops, and construction crews every week. Spare Parts
First off, let’s get one thing straight: not all spare parts are created equal. You can’t treat a $2 O-ring for a forklift the same way you treat a $2,000 hydraulic pump for a bulldozer. That’s the mistake a lot of new suppliers make—they set the same reorder point for every part and end up either wasting cash on tiny stuff or dropping the ball on the big stuff. Here’s how I break ’em down, and I know this works because I’ve tested it over a decade. I group parts into three categories, basically. The fast-movers, the slow-but-critical, and the “I hope I never sell this but if I don’t have it I’m dead” ones.
Fast-movers are your everyday stuff: filter elements, light bulbs, belts, those little gaskets that machines need every 3 months like clockwork. For these, I use something called a “fixed order quantity” but I call it the “set it and forget it” method. Wait, no, actually, I just use a simple rule: if I sell 10 of Part A every month, I never let stock drop below 5. That way, I never run out, and I’m not ordering 50 at a time. I order every time I hit that 5 mark, and since these move so quick, there’s almost no risk of them going bad or becoming obsolete. Last year, I stopped ordering 200 of my top 3 fast-movers at once and cut my excess stock on those by 40%—and I didn’t lose a single sale because I was still there when customers needed a quick top-up.
Then there’s the slow-but-critical stuff. Like, a seal kit for a specific old model of excavator that only 2 customers in my area have. They might only buy one a year, but if that excavator breaks down, they can’t wait 2 weeks for shipping—they’ll pay double just to get it same-day. For these, I don’t use numbers alone. I talk to those two customers once a quarter. I ask, “Hey, how’s that excavator holding up? Any plans to replace it soon?” If one of them is looking to sell their machine, I can cut my stock of that seal kit by half. If they’re running it nonstop, I keep one on hand at all times. I used to just stock two of these kits “just in case” and ended up with one sitting for 3 years collecting dust. Now, by checking in, I turned that extra $800 of dead stock into something I could use to buy more fast-movers that sell faster.
The third category is the “obsolete risk” parts. These are the ones for machines that the manufacturer stopped making 10 years ago, or parts that are being redesigned next year. For these, I almost never stock more than 1. I’ll have one on my shelf, and if someone needs a second, I’ll check with a few other suppliers before I order it from the manufacturer. Last time I tried stocking 3 of these, the manufacturer announced a redesign 6 months later, and I ended up selling one for a small markup and the other two for 70% off just to get rid of ’em. Now, I keep a single “emergency” unit, and that’s it. It’s a small risk, but way better than tying up cash in parts no one wants.
Next up, demand forecasting—this is where a lot of suppliers mess up, especially if they’re just using last year’s numbers. Machines don’t break down the same every year. If a factory added 5 new forklifts last year, their demand for filter elements is gonna go up this year, right? I don’t just look at 12 months of sales; I look at 24, and I ask customers about their upcoming projects. If a construction company has a big job starting in 2 months, they’re gonna need more parts for their bulldozers, so I bump up my stock on the belts and filters they use. A quick text to my regular customers every month—like, “Heads up, any big jobs coming up that might need extra parts?”—takes 5 minutes, and it’s way more accurate than any tool I tried to use a few years back. I spent $1,500 on that fancy inventory software that did all the forecasting for me, and it was wrong 30% of the time because it didn’t know my customers were launching a new warehouse. Now that I talk to ’em, I don’t need that software anymore.
Then there’s lead time—you know, how long it takes the manufacturer to send you a part. If a part only takes 3 days to get, you don’t need to stock as much. But if a part takes 6 weeks, you better keep a bigger buffer. Last year, a hydraulic part I ordered started taking 8 weeks instead of 3 because the factory in China had a labor shortage. I had adjusted my stock level based on the old lead time and almost ran out of stock for a customer who had a machine down on a job site. Now, every time a lead time changes, I update my stock level within 24 hours. I even have a little sticky note on my computer monitor that says “check lead times monthly” so I don’t forget. It’s the small stuff, but it saves me from losing big customers.
Wait, what about obsolete parts? I mentioned ’em earlier, but this is a big one for spare parts. Machines get replaced, models change, so parts that were hot 5 years ago are just sitting there now. I do a “stock audit” every 6 months. I go through every part that hasn’t sold in 12 months. If it’s not a critical part for a long-term customer, I mark it down 25% and post it on a local industrial parts Facebook group. Last audit, I had 18 parts that hadn’t moved in a year. I sold 12 of ’em in 2 months for 75% of what I paid, and only 6 ended up going to a recycling center. That’s $1,200 back in my pocket that I can use for parts that actually sell. A lot of people hate marking things down, but holding onto a part for another year just means it’s worth less and less every month.
Also, don’t sleep on your safety stock. That’s the extra stuff you keep just in case, right? But how much safety stock do you need? For fast-movers, I keep 2 weeks worth, not a month. For critical, slow parts, I keep 1. But never more. I used to keep a month’s worth of safety stock across the board and ended up with $8,000 in extra inventory that was just sitting. When I cut safety stock to 2 weeks for fast-movers and 1 for the others, that extra cash went to buying a new delivery van, which helped me get parts to customers faster and actually make more sales. It’s a balance, not a free pass to hoard stuff.
Here’s a real example from my business, too. Last year, a customer who runs a fleet of 15 delivery trucks needed a bunch of fuel injectors for an older model. I had never stocked those before, so I went through my categories. Those injectors only sell 2-3 a year in my area, but they’re critical because if a delivery truck is down, the customer loses money every day. I ordered 2 instead of 4 (my old habit would have been to order 4) and kept them behind my fast-movers. A month later, the customer called and needed a third injector—turns out another truck was having issues. I already had one, so I shipped it same-day, and they gave me a repeat order for a few more filters a week later. If I had ordered 4, I would have had one sitting for a year, but by ordering 2, I met their need and didn’t waste cash. That’s exactly the balance we’re talking about.
Another mistake I see suppliers make: only looking at their own warehouse. Sometimes, you can borrow a part from a trusted fellow supplier when you’re short, instead of ordering 10 extra. I have a few guys in the area who I swap stuff with. If I run out of a common filter, I’ll grab one from their warehouse and pay them back when my next shipment comes in. It saves both of us from stocking extra, and we all win. No need to have every single part under your own roof—networking with other suppliers is a secret hack for balancing stock.
Wait, what about digital tools? I’m not saying you shouldn’t use any tech, but keep it simple. I use a free spreadsheet (Google Sheets) to track sales, lead times, and customer orders. I color-code each part by category: green for fast-movers, yellow for slow-critical, red for obsolete. Every time someone buys a part, I update the spreadsheet, and every time I get a new shipment, I add it. That’s way easier than the fancy software I tried before, and I don’t have to pay a monthly fee. The key is consistency—update it every day, not once a month. If you slouch, the numbers get wrong, and your stock levels get off.
Let’s wrap this up with the stuff that actually matters. Balancing spare parts inventory isn’t about being perfect—it’s about being flexible. You’re not gonna get it right 100% of the time, but by grouping your parts correctly, talking to your customers, checking lead times, and doing regular audits, you’ll cut your excess stock, save cash, and still have the parts customers need when they need ’em. For me, that means less stress at 8 PM when a customer texts that a machine is down, and more cash in the bank at the end of the year.
If you’re a buyer who’s tired of dealing with stockouts or overpriced extra parts, or another supplier who wants to stop wasting money on dead inventory, hit me up to chat. I’ve got 12 years of messy, real-world experience, not just theory, and I’m happy to help you figure out what works for your business.
Inspection Rewinding Machine References
- APICS. (2020). Inventory Management Principles for Spare Parts. American Production and Inventory Control Society.
- Slack, N., & Brandon-Jones, A. (2018). Operations Management (8th ed.). Pearson Education.
- Industrial Supply Association. (2021). Best Practices for Spare Parts Inventory Optimization. Industrial Supply Association.
- Chopra, S., & Meindl, P. (2019). Supply Chain Management: Strategy, Planning, and Operation (7th ed.). Prentice Hall.
Zhejiang Deguang Machinery Co., Ltd.
Address: No.501, West Wangdong Road, Shangwang Street, Ruian City, Zhejang Province, China
E-mail: swdg@wenzhouhg.com
WebSite: https://www.deguang-machine.com/
