This is my K'nex grenade, It does need some changes though. It doesn't explode far, and it takes a med-long time to rebuild. But it does look cool!

Step 1: Get the Plastic!

Get your stuff. Read the list or look at the pics, or both. You decide!
))>>{CONNECTORS}<<((
x16 Green connectors and x2 Metallic greens.
x4 Orange (Black version) connectors.
x3 Dark grey connectors.
x2 Red connectors (Granite version).
x1 A pile of sharpanel of your choice.
x1 Light grey connector.
x2 Snowflake conenctors (Black version).
x8 Yellow connectors (Grey version).

))>>{RODS}<<((
x18 Green rods.
x5 White rods.
x1 Blue rod.
x1 Yellow rod.

))>>{MISC.}<<((
x1 Tiny blue connector.
x1 Blue ring.
x1 Y connector.
x3 Rubber bands.

Now that we have all the parts, let's have some FUN!

Step 2: The Body

We will make the body now!

Pic #1: Get this stuff.
Pic #2: Make these.
Pic #3: Get these things.
Pic #4: Make this.
Pic #5: Make 7 more.

Good! Good! We made the body!!! Now we will make the pin next!

Step 3: Pins & Needles

Let's make the pin shall we?

Pic #1: Get these.
Pic #2: Make this, and save the Y connector for later.

That was easy... Now we make the handle!

Step 4: Ze Handle

You can use the handle to clip the grenade onto your pants!
We will build it now!

Pic #1: Get all this stuff.
Pic #2: Make this.
Pic #3: Slip the pin in here.
Pic #4: Slip a blue rod through here and add some grey connectors like this.
Pic #5: Another view.
Pic #6: Don't forget to add the green rods onto the red connectors!

We made the handle, now we put it all together! MUHAHAHAHAAA!

Step 5: Putting It All Together

Now we will put it together!

Pic #1: Get this junk- I mean stuff.
Pic #2: Attach this onto that.
Pic #3: Slide the pin into the hole.
Pic #4: Push the green rods on the handle into the green connectors.
Pic #5: Add your shrapnel.
Pic #6: Add the bottom to keep the shrapnel in.
Pic #7: Push on the snowflake connector on the bottom to make room for the Y connector to fit on to the yellow rod.
Pic #8: Attach the Y connector to the yellow rod.
Pic #9: Put rubber bands around the center.

Now that it's built, you may explode the grenade. All you need to do is pull the handle off the grenade and throw. Have fun :)