Exhibit 4.13

SHARE SALE AND PURCHASE AGREEMENT

dated
as of 11 March, 2003

by
and between

Spirent B.V., a limited company organized under the laws of the Netherlands, with registered offices at Blaak 16, 6th floor
3011 TA Rotterdam

(hereinafter
referred to as the"Seller")

on
the one hand

and

Hohorst Familien Holding (Schweiz) Beteiligungs GmbH, a private limited company under the laws of Germany, registered in the commercial register of the
local court of Minden, Germany, under the registration number 2914, with its headquarters at Hansastrasse 27, 32423 Minden, Germany

(hereinafter
referred to as the"Purchaser 1")

and

Hohorst Familien Holding (Minden) Beteiligungs GmbH, a private limited company under the laws of Germany, registered in the commercial register of the
local court of Minden, Germany, under the registration number HRB 2913, with its headquarters at Hansastrasse 27, 32423 Minden, Germany

(hereinafter
referred to as the"Purchaser 2")

on
the other hand

for
the sale and purchase of 306 registered shares ofWago Contact SA, 1564 Domdidier, Switzerland (hereinafter referred to as the "Company").

WHEREAS:

---

NOW, THEREFORE, Seller and Purchasers (the "Parties")agree as follows:

1.     DEFINITIONS



2

---



2.     SALE AND PURCHASE OF SHARES

Account no.:

57844446Type of Account:

Swiss Fran AccountBank (the "Bank"):

HSBC International DivisionSort Code:

40-05-15SWIFT Code:

MID LGB 22Beneficiary:

Spirent plc.




3

---

3.     CLOSING AND CLOSING MATTERS

4

---

4.     CONDITIONS PRECEDENT

5

---

5.     REPRESENTATIONS, WARRANTIES AND COVENANTS

6

---



6.     REMEDIES FOR BREACH OF REPRESENTATIONS AND WARRANTIES OF SELLER

7

---

7.     COSTS AND EXPENSES, TAXES

8.     TERMINATION OF AGREEMENT, CUT-OFF DATE

8

---

9.     NON-SOLICITATION

The Parties hereby agree that for a period of three years following the Closing Date or one year following termination of the trading relationship between WAGO
Kontakttechnik GmbH on the one hand and Spirent and certain of its affiliates as per Exhibit 9 on the other handwhatever occurs laterthey
shall not, and shall cause their affiliates not to



10.   GENERAL PROVISIONS

9

---

10

---

| |     |                    |                                                                                                                                                            
| | --- | ------------------ | -----------------------------------------------------------------------------------------------------------------------------------------------------------
| | (a) | If to Seller:      | Spirent B.V.,
attn. Mr. George Frederik Nicolai
Blaak 16, 6th Floor
3011 TA
Rotterdam
Telefax: 0031 1 04 300 904                                           
| |     | With copy to:      | Spirent plc
Spirent House, Crawley Business Quarter
Fleming Way
Crawley
West Sussex RH10 2QL
United Kingdom
Attn. General Counsel
Telefax: 0044 1293 767677
| | (b) | If to Purchaser 1: | Hohorst Familien Holding (Schweiz) Beteiligungs GmbH
Attn. Mr. Wolfgang Hohorst
Schilfgrund 13
32429 Minden, Germany
Telefax: 0049  571  38 56 941       
| | (c) | If to Purchaser 2: | Hohorst Familien Holding (Minden) Beteiligungs GmbH
Attn. Mr. Wolfgang Hohorst
Schilfgrund 13
32429 Minden, Germany
Telefax: 0049  571  38 56 941        

11.   GOVERNING LAW AND ARBITRATION

11

---

IN WITNESS WHEREOF,the Parties hereto have executed this Agreement in one original as of the date and year first above written.

|                                                                                           |  |                     
|------------------------------------------------------------------------------------------ |  | --------------------
|Spirent B.V.
By:                                                                           |  |                     
|                                                                                           |  |                     
|Dr. Björn-Axel Dißars, acting pursuant to the power of attorney attached to this Agreement
|Hohorst Familien Holding (Schweiz) Beteiligungs GmbH                                      
|                                                                                           |  |                     
|Wolfgang Hohorst                                                                           |  | Sven-Michael Hohorst
|Hohorst Familien Holding (Minden) Beteiligungs GmbH                                       
|                                                                                           |  |                     
|Wolfgang Hohorst                                                                           |  | Sven-Michael Hohorst
|Dr. Ulrich Hartmann, notary, who accepts the instructions given to him in this Agreement  
|                                                                                           |  |                     

12

---



Exhibit 1.1

List of Shares

13

---

Exhibit 1.2  1.6

Copies of the Share Certificates

14

---

Exhibit 4.1.5

Guarantee on first demand by Spirent plc.

[Letterhead
of Spirent plc.]

Guarantee

Spirent
BV, a limited company under the laws of the Netherlands with registered offices at Blaak 16, 6th floor, 3011, TA Rotterdam (the "Seller");

and

Hohorst
Familien Holding (Schweiz) Beteiligungs GmbH, a private limited company under the laws of Germany, registered in the commercial register of the local court in Minden under the registration
number HRB 2914 and with its headquarters at Hansastrasse 27, 32423 Minden (the "Purchaser 1");

and

Hohorst
Familien Holding (Minden) Beteiligungs GmbH, a private limited company under the laws of Germany, registered in the commercial register of the local court in Minden under the registration
number HRB 2913 and with its headquarters at Hansastrasse 27, 32423 Minden (the "Purchaser 2").

(Purchaser
1 and Purchaser 2 jointly the "Purchasers").

have
entered into an agreement for the sale and transfer of shares in WAGO Contact SA (the "Agreement").

We,
Spirent plc, hereby give a guarantee ("Bürgschaft") to the Purchasers, being joint and several creditors, for all claims for payment
that the Purchasers may have against the Seller under the Agreement.

This
guarantee is limited to an amount of CHF 7,415,000,000.

This
guarantee is payable on the Purchasers' first written demand specifying the amount and legal cause of the Purchasers' claim against the Seller and stating that the Seller has failed to comply
with its payment obligation in respect thereof.

This
guarantee shall expire when this document is returned to us by or with the consent of the Purchasers or on 31 December 2007, whichever occurs earlier, unless a demand for payment
hereunder, complying with the provisions of the preceding paragraph, has been received by us on or before that date.

This
document shall be returned to us immediately upon expiry of our guarantee.

Any
rights or obligation arising out of this guarantee may only be transferred to a third party with our prior written consent; Section 354a German Commercial Code remains unaffected. We hereby
explicitly and irrevocably agree to the assignment of rights to Dresdner Bank AG, Bielefeld.

This
guarantee shall be subject to German law. Any disputes arising out of or in connection with this guarantee shall be settled by arbitration in accordance with the UNCITRAL Arbitration Rules in
effect on the date hereof. The appointing authority shall be the President of the Hamburg Court of Appeals (Präsident des Oberlandesgerichts in
Hamburg). The number of arbitrators shall be three. The place of arbitration shall be Hamburg. The language that may be used in the arbitral proceedings shall be German or
English.

15

---

In
the event that any provision of this guarantee should be ineffective, this shall not affect the validity of the remainder hereof.

This
guarantee is subject to and shall be governed in accordance with German law.

|             |  |             
|------------ |  | ------------
|[...], [...] |  |             
|             |  |             
|             |  | Spirent plc.
|             |  | by:         

16

---

Exhibit 4.1.8

Form of a Legal Opinion

17

---

Exhibit 4.1.9

Confirmation of Spirent

18

---

Exhibit 9

List of Affiliates

19

---

QuickLinks