Model Rocket Delay Kit Guide: HDK-11 and CRDK38-06 Explained
By Quest Q-jet | Published: 2026-10-13
Category: Buying Guides
Match your delay kit to the exact RMS motor before you buy. This guide explains HDK-11 and CRDK38-06 fit, delay grain counts, and compatibility rules.
Quick answer
Buy the delay kit that matches your exact RMS motor and power class, not just the diameter. Choose the HDK-11 for E18-4W and F24-4W motors, and the CRDK38-06 for the RMS-38 H550ST Super Thunder reload using the 14 second adjustable delay. Hobby and High Power delay kits are not interchangeable, so verify the motor designation before ordering.
Why delay kits are motor-specific
An RMS delay kit is not a universal spare. Each kit is built for a specific reload motor and delay length, and the parts inside are matched to that assembly. The HDK-11 is listed for E18-4W (51804) and F24-4W (62404) motors, while the CRDK38-06 is listed for the RMS-38 H550ST Super Thunder reload using the 14 second adjustable delay. If you order by diameter alone, you can end up with a kit that will not seat or time correctly.
What comes in each delay kit
The CRDK38-06 includes 1 rocket motor delay element plus insulators and spacers if needed. The HDK-11 is a 3-pack that includes 3 rocket delay elements and spacers. In both cases, delay O-rings, delay insulators, and other motor parts are supplied with the RMS reload kits, so you are buying the wear or replacement items rather than a full motor rebuild set.
Choosing by delay length and motor class
Start with the motor designation printed on your reload kit or hardware. The number after the dash is the delay length in seconds, so an E18-4W uses a 4 second delay and the H550ST kit is set up for a 14 second adjustable delay. Match that number, then confirm the power class. High Power RMS reload delay kits are not compatible with Mid Power RMS products, and Hobby Delay Kits and High Power Delay Kits are not interchangeable.
Hardware and shipping notes
Delay kits do not include motor hardware. For the K1275R-PS RMS-54/2560 reload kit, you need AeroTech RMS-54/2560 motor hardware to build and complete the motor, and assembly requires installing a forward seal disc (54FSD). Hardware is sold separately as a complete set or as individual parts. The HDK-11 is U.S. mailable with no hazmat fee, which makes it simpler to restock than high power motor components.
Decision rules for buying a delay kit
- Match the motor designation first: Read the reload kit label and find the exact motor, such as E18-4W or H550ST, before choosing a delay kit. If the motor is not listed on the delay kit, do not buy it.
- Check the delay length: The number after the dash is the delay in seconds; the CRDK38-06 is for a 14 second adjustable delay. Wrong delay length changes ejection timing.
- Stay within the power class: Hobby Delay Kits and High Power Delay Kits are not interchangeable, and High Power RMS delay kits are not compatible with Mid Power RMS products. Never substitute across Mid Power and High Power.
- Count your flights: The HDK-11 includes 3 delay elements, while the CRDK38-06 includes 1. Buy the quantity that matches your launch schedule.
- Plan for hardware: Reload kits like the K1275R-PS need separate RMS-54/2560 hardware and a 54FSD forward seal disc. Order hardware and the seal disc with the reload, not after.
Delay kit and reload facts
- AeroTech RMS-38 H550ST Super Thunder Complete Reload Delay Kit - CRDK38-06: The AeroTech RMS-Plus CRDK38-06 is for use with RMS-38 H550ST Super Thunder reload motors using the 14 second adjustable delay, and comes with 1 rocket motor delay element plus insulators and spacers if needed. If you fly the H550ST, this is the matching delay kit; other delay parts come with the RMS reload kit.
- AeroTech HDK-11 RMS-24/40 Hobby Delay Kit (3-Pack) - 43511: The AeroTech HDK-11 is for use with E18-4W (51804) and F24-4W (62404) motors and comes with 3 rocket delay elements and spacers. A 3-pack covers three flights on those specific motors, and it ships U.S. mailable with no hazmat fee.
- AeroTech K1275R-PS RMS-54/2560 Reload Kit (1 Pack) - 111275P: The AeroTech K1275R-PS RMS-54/2560 reload kit requires AeroTech RMS-54/2560 motor hardware and a forward seal disc (54FSD) during assembly. Budget for hardware and the seal disc separately; the reload kit alone will not complete the motor.
- AeroTech F63-10R RMS-24/60 Reload Kit (2 Pack) - 66310: The AeroTech F63-10R RMS-24/60 reload kit requires AeroTech RMS-24/60 motor hardware, and Mid Power RMS reload kits are not compatible with High Power RMS products. Confirm your hardware size before buying reloads or delay kits, because crossing power classes will not work.
Is a delay kit the right buy for you?
Best for
- Flyers who already own the matching RMS motor hardware and reload kits
- Restocking delay elements for E18-4W, F24-4W, or H550ST Super Thunder flights
- Buyers who want a U.S. mailable, no-hazmat-fee option like the HDK-11
Not for
- Anyone who has not confirmed the exact motor designation and power class
- Flyers expecting a delay kit to include motor hardware or a full reload
- Users trying to cross Mid Power and High Power RMS parts
